Meteorite Mineralogy
- Alan E. RubinAlan E. RubinUniversity of California Los Angeles
- and Chi MaChi MaCalifornia Institute of Technology
Summary
Meteorites are rocks from outer space that reach the Earth; more than 60,000 have been collected. They are derived mainly from asteroids; a few hundred each are from the Moon and Mars; some micrometeorites derive from comets. By mid 2020, about 470 minerals had been identified in meteorites. In addition to having characteristic petrologic and geochemical properties, each meteorite group has a distinctive set of pre-terrestrial minerals that reflect the myriad processes that the meteorites and their components experienced. These processes include condensation in gaseous envelopes around evolved stars, crystallization in chondrule melts, crystallization in metallic cores, parent-body aqueous alteration, and shock metamorphism. Chondrites are the most abundant meteorites; the major components within them include chondrules, refractory inclusions, opaque assemblages, and fine-grained silicate-rich matrix material. The least-metamorphosed chondrites preserve minerals inherited from the solar nebula such as olivine, enstatite, metallic Fe-Ni, and refractory phases. Other minerals in chondrites formed on their parent asteroids during thermal metamorphism (such as chromite, plagioclase and phosphate), aqueous alteration (such as magnetite and phyllosilicates) and shock metamorphism (such as ringwoodite and majorite). Differentiated meteorites contain minerals formed by crystallization from magmas; these phases include olivine, orthopyroxene, Ca-plagioclase, Ca-pyroxene, metallic Fe-Ni and sulfide. Meteorites also contain minerals formed during passage through the Earth’s atmosphere and via terrestrial weathering after reaching the surface. Whereas some minerals form only by a single process (e.g., by high-pressure shock metamorphism or terrestrial weathering of a primary phase), other meteoritic minerals can form by several different processes, including condensation, crystallization from melts, thermal metamorphism, and aqueous alteration.
Introduction
In mid 2020, about 470 minerals had been identified in meteorites (Appendix), amounting to about 8–9% of the total number of well-characterized mineral phases. Meteorite mineral species include native elements, metals and metallic alloys, carbides, nitrides and oxynitrides, phosphides, silicides, sulfides and hydroxysulfides, tellurides, arsenides and sulfarsenides, halides, oxides, hydroxides, carbonates, sulfates, molybdates, tungstates, phosphates and silico phosphates, oxalates, and silicates from all six structural groups.
Each meteorite group has a distinctive set of pre-terrestrial minerals that reflect the myriad processes that the meteorites and their components experienced. These processes include: (a) condensation in gaseous envelopes around evolved stars, (b) condensation in the solar nebula, (c) crystallization in CAI melts, (d) crystallization in melted portions of ameboid olivine inclusions (AOIs), (e) crystallization in chondrule melts, (f) exsolution during the cooling of Ca-Al inclusions (CAIs) or refractory inclusions, (g) exsolution during the cooling of chondrules, (h) exsolution during the cooling of opaque assemblages (including so-called “metallic chondrules” in type-3 ordinary chondrites as well as subrounded metal- and sulfide-rich nodules in type-3 enstatite chondrites), (i) annealing of amorphous material in the solar nebula, (j) annealing of amorphous material on parent bodies, (k) thermal metamorphism and exsolution, (l) aqueous alteration, hydrothermal alteration and metasomatism, (m) precipitation from asteroidal brines, (n) shock metamorphism, (o) space weathering, (p) condensation within impact plumes, (q) crystallization from melts in differentiated or partially differentiated bodies, (r) condensation from late-stage vapors in differentiated bodies, (s) exsolution, inversion and subsolidus redox effects within cooling igneous materials, and (t) solar heating near perihelion. In addition, meteorites contain minerals formed during passage through the Earth’s atmosphere and via terrestrial weathering after reaching the surface.
Some meteoritic minerals form by only a single mechanism, for example, ringwoodite and ahrensite by high-pressure shock metamorphism of olivine; other minerals form by several mechanisms such as olivine by (a) condensation around red giant and asymptotic giant branch (AGB) stars, (b) condensation in the solar nebula, (c) crystallization in melted portions of CAIs and AOIs, (d) crystallization in chondrule melts, (e) thermal metamorphism, (f) crystallization from impact melts, (g) condensation within impact plumes, (h) crystallization in magmatic bodies on differentiated asteroids, (i) annealing of amorphous material, (j) crystallization in fusion crusts, and (k) aqueous alteration.
Meteorite Classification
Meteorites are derived from asteroids, the Moon, and Mars (Figure 1). Some asteroids melted, presumably due to the decay of short-lived nuclides such as 26Al (t½ = ~720,000 years) and/or to energetic collisions. These bodies separated into different layers comprised of immiscible melts; the densest liquids sank to the core with less dense liquids emplaced above them. These melted asteroids are thus differentiated bodies and the samples derived from them are differentiated meteorites. (Like these melted asteroids, the Earth, Moon, and Mars are all differentiated bodies.) Differentiated meteorites include iron meteorites (most of which are derived from the metallic cores of differentiated asteroids), stony-irons (one class of which is derived from the core–mantle boundaries of these asteroids), and stony meteorites (igneous rocks) hailing from the crust and mantle. Differentiated stony meteorites are also called achondrites because they lack the submillimeter-sized igneous spherules called “chondrules,” commonly found in abundance in undifferentiated (chondritic) meteorites.
Figure 1. Classification of meteorite groups.
Many of the differentiated meteorites are thought to be from the asteroid 4 Vesta. These groups include eucrites (basalts) derived from the crust, diogenites (orthopyroxenites) derived from the lower crust and/or upper mantle, and howardites (mechanical mixtures called breccias) made up of fragments of these two groups.
Iron meteorites are classified by chemical composition into groups with names beginning with a Roman numeral and ending in one or two letters. Examples include groups IAB, IIE, IIIAB, and IVA. Each is presumed derived from a separate parent asteroid—magmatic irons from asteroidal cores, and non-magmatic irons, perhaps from impact melts close to the asteroid surface.
The chondritic meteorites are from asteroids that never experienced widespread melting. They retained more of the textural, mineralogical, and compositional properties their precursor components acquired from the solar nebula (the cloud of gas and dust from which the solar system sprang) when they accreted.
Meteorite classifications are complex. Chondrites are divided into several broad classes including ordinary chondrites (constituting ~80% of all meteorites), carbonaceous chondrites (some of which are rich in bulk carbon and hydroxyl-bearing mineral phases), and enstatite chondrites (highly reduced samples rich in the Mg-rich silicate mineral enstatite (MgSiO3)). Each of these classes comprises two or more groups, distinguished by a restricted set of mineralogical, textural, and chemical properties. Ordinary chondrites comprise the H, L, and LL groups (standing for high total iron, low total iron, and low total iron and low metallic iron, respectively). Carbonaceous chondrites include eight major groups, typically named after their prototype; CI chondrites are samples related to the meteorite Ivuna, CM—Mighei, CO—Ornans, CV—Vigarano, CK—Karoonda, CR—Renazzo, CH—high-iron group, CB—Bencubbin. R and K chondrites are less abundant groups with their own sets of distinctive properties.
Chondrites underwent different degrees of thermal metamorphism. Those rocks least affected are the petrologic type-3 chondrites; those most thoroughly metamorphosed are petrologic type 6. Many carbonaceous chondrites have been aqueously altered on their parent asteroids: type-3 chondrites experienced little alteration, type-2 chondrite are significantly altered, and type-1 chondrites are extensively altered.
Mineralogy of Meteorite Groups
Chondrites
Ordinary Chondrites
The least-metamorphosed type-3 ordinary chondrites (OCs) consist of a few basic components: (a) chondrules, chondrule fragments, and coarse isolated monocrystalline and polycrystalline grains and grain fragments, (b) opaque phases—principally metallic Fe-Ni (low-Ni metal (known as kamacite) and taenite) and sulfide (troilite, rare examples of which contain daubréelite exsolution lamellae),1 (c) fine-grained silicate matrix material, including organic components and tiny presolar grains, (d) rare refractory inclusions (CAIs) and fragments, and (e) rare ameboid olivine inclusions—AOIs (also known as amoeboid olivine aggregates—AOAs). Some type-3 OC breccias also include foreign clasts that are fragments (mainly CM chondrites) derived from different asteroids. Matrices in aqueously altered type-3 OC, such as the meteorite Semarkona, contain additional opaque minerals: magnetite, Ni-rich metal (mainly awaruite), Ni-rich sulfide (pentlandite), and Fe carbide (cohenite, haxonite, edscottite).
The primary minerals in unaltered portions of the least-equilibrated OC include olivine, low-Ca pyroxene (major clinoenstatite and rare orthopyroxene), kamacite, taenite, troilite and, nearly exclusively within chondrules, crystallites of Ca-pyroxene, pigeonite, and rare tiny grains of merrillite. Rare small grains of primary chromite occur in some Type-II (FeO-rich) chondrules. Rare CAIs, AOIs, and presolar grains each have their characteristic allotment of refractory phases.
New mineral phases that appear in OC during parent-body thermal metamorphism include orthopyroxene, Ca-pyroxene, plagioclase, phosphate, chromite, ilmenite, and rutile:
Low-Ca pyroxene. Type-IB (low-FeO) porphyritic pyroxene chondrules (i.e., chondrules with coarse grains) in unequilibrated type-3 OC (e.g., type 3.0–3.5) contain low-Ca clinopyroxene phenocrysts (large grains that crystallized from the chondrule melt during solidification), exhibiting polysynthetic twinning on (100) (numerous thin lamellae aligned along a particular crystallographic direction), inclined extinction, and shrinkage cracks perpendicular to the twinning planes. These phenocrysts formed as a metastable phase by inversion from protoenstatite (the stable polymorph (a mineral with the same composition as another mineral but possessing a different crystal structure) between 1,000 and 1,557ºC) with an accompanying change in volume during chondrule quenching. At a temperature of ~630ºC, clinoenstatite transforms into (ortho)enstatite, accounting for the absence of low-Ca clinopyroxene in unshocked type-5 and type-6 OC.
Ca-pyroxene. In type-3.0–3.5 OC, Ca-pyroxene is present mainly in chondrules, where it occurs as small crystallites within the mesostasis (residual melt) and as overgrowths (grains growing on top of other grains) on low-Ca pyroxene phenocrysts. (It also occurs in rare CAIs.) Ca-pyroxene is essentially absent within fine-gained silicate matrix material in type-3 OC. With increasing thermal metamorphism, Ca-pyroxene increases in size from submicrometer grains in type-4 OC, to 2–5-µm grains in type-5 OC, and to grains tens of micrometers in size in type-6 OC.
Plagioclase. Relatively coarse grains of plagioclase are very rare in type 3.0–3.5 OC, except for anorthite phenocrysts in rare Al-rich chondrules, small oligoclase grains within igneous rims around ~10% of chondrules, and in very rare CAIs and AOIs. During thermal metamorphism, chondrule mesostases devitrify (evident in type 3.7–3.9 OC), and albite crystals nucleate and grow. Type-5 OC contain 2–10 µm-size plagioclase grains; type-6 OC contain many plagioclase grains exceeding 50 µm.
Phosphate. The mesostases in Type-II chondrules in LL3.0 Semarkona average ~1.3 wt.% P2O5 and contain 2–10 µm grains of merrillite. Although the mesostases in Type-I chondrules have lower concentrations of P2O5 (<0.02 wt.%), some of these chondrules contain similarly sized merrillite grains. These small phosphate grains crystallized within the mesostasis during chondrule cooling. Type-3 and type-4 OC contain fine-grained merrillite and/or chlorapatite within troilite-metal assemblages; chlorapatite also occurs as 2–15 µm-thick rinds around some kamacite and taenite grains. In these cases, the source of the P is probably adjacent metallic Fe-Ni. Phosphate grains in the matrix are tens of micrometers in size; some grains are as large as 300 µm.
Chromite. Chondrules in type-3 OC contain some small chromite grains up to ~10 µm in size. Coarse secondary chromite grains (up to 200 µm) within unshocked type-4–6 OC occur as isolated grains and in association with metallic Fe-Ni and troilite.
Ilmenite and rutile. Type-3 OC do not contain coarse grains of ilmenite or rutile, but such grains are present in some type-5 and type-6 OC. In Farmington (a shock-darkened L5 chondrite), ilmenite occurs in ~500 µm-size clusters that also include chromite, metallic Fe-Ni, and troilite. Some of these ilmenite grains contain rutile exsolution lamellae; others have exsolution lamellae of both rutile and chromite. The type-5 H-chondrite Allegan contains discrete grains of rutile in the matrix, not associated with ilmenite or chromite.
In each OC group, there is an apparent systematic increase in oxidation state with petrologic type. These include (a) increasing FeO/(FeO+MgO) in olivine and low-Ca pyroxene, (b) increasing kamacite (low-Ni metallic Fe) Co, and Ni contents, (c) decreasing modal metallic Fe-Ni abundance, and (d) increasing normative olivine/pyroxene ratio (due to the replacement of low-Ca pyroxene by ferroan olivine). These correlations are probably due to the presence of minor amounts of water, likely bound within phyllosilicates. With increasing heat (radiogenic and/or collisional) phyllosilicates were dehydrated; water was driven out of the crystal lattices and became available as an oxidant.
R Chondrites
Most R chondrites are of petrologic type ≥3.6 and contain abundant olivine (53–77 vol.%) with a sharp compositional peak at Fa37-40 (i.e., 37–40 mol% of the fayalite (Fe2SiO4) component of olivine). Nevertheless, the total range in Fa is broad: 0.4–45.4 mol%. Low-Ca pyroxene tends to be much less abundant (~0-13 vol.%) and is essentially absent in Y 793575. In R chondrites with low-Ca pyroxene, this phase is monoclinic and commonly exhibits polysynthetic twinning. It also tends to be compositionally heterogeneous: for example, the compositional distribution in the meteorites Rumuruti and PCA 91002 is Fs~0-30. Other pyroxene phases in R chondrites include pigeonite, augite, and diopside. Plagioclase is mostly sodic, in the compositional range of albite or oligoclase (An6-18 (i.e., 6–18 mol% of the anorthite (CaAl2Si2O8) component of the mineral plagioclase)). More-calcic grains (An35-69) are present in the meteorite Acfer 217; rare potassic grains occur in Acfer 217 (An7.9Or46.4) and Rumuruti (An4.2Or87.3).
Primary minerals within the rare CAIs include spinel, hibonite, Al-Ti diopside, perovskite, anorthite, and accessory olivine. Nepheline, sodalite, and ilmenite were formed in some CAIs as secondary minerals during parent-body aqueous alteration.
Matrix material is abundant in R chondrites. It contains small grains of ferroan olivine (Fa35-60) and low-Ca pyroxene, chondrule fragments, and isolated mafic silicate grains. Opaque phases include sulfides (pyrrhotite, troilite, pentlandite, chalcopyrite, pyrite, rare lead sulfide, rare arsenic sulfide), oxides (magnetite, chromite, Al-rich chromite, magnetite-chromite solid solution, ilmenite), phosphates (chlorapatite, hydroxylapatite, merrillite), rare metallic Fe-Ni (awaruite, kamacite, martensite), rare metallic Cu, rare noble-metal-rich phases (PtFe(Ir,Ni) alloy, Pt metal, Os with minor Re, Pt, Os-Ir-Ru-Pt alloy, native Au, electrum, ruthenosmiridim, rustenburgite, PdPtSn), and very rare small grains of noble-metal-rich sulfides (erlichmanite, laurite, Os, Ru, Fe-rich sulfide), arsenides (sperrylite), sulfarsenides (irasite, (IrPt)AsS), and tellurides (chengbolite, moncheite).
Three R6 chondrites have OH-bearing phases: MIL 11207 and LAP 04840 contain hornblende and phlogopite; MIL 07440 contains accessory titan-phlogopite, but no hornblende.
Carbonaceous Chondrites
Carbonaceous chondrites comprise more individual groups than any other meteorite class. They contain eight major groups, a few grouplets, and more than a dozen unique samples. These groups and grouplets can be distinguished from each other by numerous physical and chemical properties, including mineralogy, texture, chondrule size, chondrule abundance, bulk chemical composition, and O-isotopic composition.
CI Chondrites
The principal pre-terrestrial mineral constituents of CI chondrites include: (a) Fe-Mg serpentines (hydrous minerals that crystalize in sheet-like structures) with interlayered saponite, (b) magnetite and tiny grains of ferrihydrite, (c) carbonates (dolomite, breunnerite, siderite, calcite), (d) sulfides (pyrrhotite, rare elemental S, pentlandite, cubanite), and (e) miscellaneous accessory phases (merrillite, periclase, Ti3O5, magnesiochromite, eskolaite). There are also rare isolated grains of olivine (some containing 2–5 µm-size spheroids of metallic Fe-Ni, some containing silicate melt inclusions with shrinkage bubbles), low-Ca pyroxene (mainly orthoenstatite), and Ca-pyroxene, all probably derived from fragmented chondrules. Small rare grains of hibonite and spinel were probably broken out of altered CAIs. Presolar grains include graphite, diamond, silicon carbide, and corundum.
CM Chondrites
These meteorites average ~60 vol.% fine-grained matrix material. In unweathered CM samples, the matrix consists of abundant Fe-Mg serpentines (mainly Fe-bearing chrysotile), variable amounts of isolated clumps of tochilinite/cronstedtite intergrowths, minor metallic Fe-Ni, some sulfide (pyrrhotite, pentlandite and grains of intermediate composition, murchisite), oxide (small clumps of magnetite and rare hematite), carbonate (calcite and complex carbonate phases containing Ca, Mg, Fe, Mn, and Ni) and accessory forsterite, Cl-free apatite, orthoenstatite, Ca-pyroxene, halite, and sylvite (Figure 2).
Figure 2. Back-scattered electron (BSE) images showing (a) clumps of tochilinite/cronstedtite intergrowths, and (b) magnetite of different morphologies (quasi-equant grains, spherulites, and framboids) occurring together with spherules of apatite in the matrix of the Murchison CM2 chondrite.
There are additional components in CM chondrites:
Chondrules and chondrule fragments. They contain major olivine and low-Ca clinopyroxene with a few blebs of metallic Fe-Ni; some metal-free chondrules contain small grains of sulfide. A few chondrules in the least-altered CM chondrites (e.g., the meteorite named Paris) contain isotropic glassy mesostases.
CAIs. CM refractory inclusions can be classified by their principal minerals: spinel-pyroxene, spinel, spinel-pyroxene-olivine, pyroxene, pyroxene-olivine, hibonite-bearing. The olivine is forsteritic. Pyroxene phases include diopside, Al-rich diopside, Al-Ti diopside, and rare enstatite. Some CAIs contain small grains of perovskite. Only rare CAIs contain gehlenitic melilite. There are also rare ultrarefractory inclusions in CM chondrites containing Y-rich perovskite, hibonite, Sc-rich and Ti-rich clinopyroxene, davisite, panguite, thortveitite, and machiite (Figure 3). Although some workers have suggested that CM CAIs formed in the solar nebula with little melilite (in contrast to CAIs in CV chondrites), it seems more likely that the abundant melilite initially present in CM CAIs was mostly destroyed by early-stage parent-body alteration. It was replaced by phyllosilicates, voids, and zeolite-like Na-Al silicates.
AOIs. These objects contain major forsterite enclosing pores and minor wormy patches of diopside and accessory Al-rich diopside.
Presolar grains. Presolar grains in CM chondrites resemble those in other primitive carbonaceous-, ordinary-, and enstatite-chondrite groups.
Figure 3. (a) An ultrarefractory inclusion containing primary thortveitite (Sc2Si2O7), panguite [(Ti4+,Sc,Al,Mg)1.8O3], davisite (CaScAlSiO6), and Sc,Al,Ti-diopside from the Murchison CM2 chondrite (Ma, Beckett, Tschauner, & Rossman, 2011). (b) Ultrarefractory machiite [(Al,Sc)2(Ti,Zr)3O9] with corundum in the matrix of the Murchison CM2 chondrite (Krot, Nagashima, & Rossman, 2020). BSE images.
CO Chondrites
Chondrules in primitive CO3 chondrites contain major olivine, clinoenstatite, and feldspathic glass. Many clinoenstatite grains are polysynthetically twinned and have Ca-pyroxene overgrowths; pigeonite is also present. Type-I chondrules contain appreciable metallic Fe-Ni and minor sulfide. Spinel is present in Type-I chondrules; chromian hercynite occurs in Type-II chondrules. In more-metamorphosed CO chondrites, anorthite grains (in many cases intergrown with nepheline) occur within the mesostasis.
Amoeboid olivine inclusions in CO3.0 chondrites contain major forsterite, anorthite, Al-Ti diopside (fassaite), and opaque phases (mainly kamacite). A few AOIs also contain spinel. Troilite is rare to absent. AOIs contain 8–20 vol.% voids. The AOIs in CO3.3–3.8 chondrites consist of forsterite, anorthite, Al-Ti diopside, opaque phases (kamacite, taenite, troilite), spinel, pleonaste, Ca-phosphate (probably merrillite), and voids.
The primary minerals within CAIs include melilite, spinel, clinoenstatite, diopside, Al-Ti diopside, forsterite, hibonite, anorthite, kamacite, perovskite and rare corundum, and grossite; secondary CAI minerals include hercynite, nepheline, sodalite, ilmenite, monticellite, and troilite. Rare ultrarefractory inclusions contain Y-rich perovskite, davisite, grossmanite, warkite, eringaite, kangite, and silicate glass with significant concentrations of TiO2, Sc2O3, Y2O3, and ZrO2.
The primary phases in CO3 matrix material include Si-rich and Fe-rich amorphous silicate, olivine, low-Ca pyroxene, and metallic Fe-Ni. Secondary phases include magnetite, pentlandite, pyrrhotite, anhydrite, ferric oxide, Fe-Mg serpentine, and chlorite.
There are several opaque phases: metallic Fe-Ni (kamacite, taenite, tetrataenite), sulfide (troilite, pentlandite), carbide (haxonite, cohenite), and oxide (magnetite, chromite). Some Type-I chondrules in the meteorite Ornans contain magnetite intergrown with tiny Ca-phosphate grains.
CV Chondrites
The group is divided into three subgroups: the reduced subgroup (CV3Red), the Allende-like oxidized subgroup (CV3OxA), and the Bali-like oxidized subgroup (CV3OxB), each with a distinguishable set of secondary minerals.
The reduced-subgroup members are the most pristine; their chondrules consist mainly of olivine, low-Ca pyroxene, glass, and droplets of metallic Fe-Ni (kamacite and taenite). Additional primary phases in these rocks include: (a) troilite mainly in chondrules and matrix and (b) anorthite, gehlenite, spinel, diopside, Al-Ti diopside (fassaite), perovskite, and hibonite in CAIs (and, to a lesser, extent AOIs). There are other primary refractory phases that occur in accessory amounts in CAIs, including davisite, grossmanite, and rubinite (Figure 4). Presolar grains in reduced CV chondrites include diamond and silicon carbide. There are some secondary minerals in CV3Red samples, perhaps introduced during brecciation: these phases include minor saponite, serpentine, and ferrihydrite in Vigarano.
Figure 4. Rubinite (Ca3Ti3+2Si3O12) and grossmanite (CaTi3+AlSiO6) in a compact Type A CAI from the Efremovka CV3 chondrite. After Ma et al. (2017). BSE image.
Oxidized subgroups contain both primary and secondary phases. There are many primary refractory phases that occur in accessory amounts in CAIs, including grossite, corundum, allendeite, burnettite, davisite, grossmanite, hexamolybdenum, kangite, krotite, kushiroite, panguite (Figure 5), paqueite, rubinite, warkite, and (in a single CAI from Allende) dmisteinbergite. Secondary phases in CVOxA chondrites include magnetite, Ni-rich sulfide, ferroan olivine (Fa30-60), nepheline, sodalite, tetrataenite, awaruite, merrillite, monticellite, kirschteinite, hutcheonite, andradite, dmisteinbergite, grossular, hedenbergite, wollastonite, butianite, and nuwaite (Figure 6). Secondary phases in CVOxB chondrites include phyllosilicate (Fe-bearing saponite, Mg-rich saponite, Fe-rich serpentine), magnetite, Ni-rich sulfide, fayalitic olivine (Fa95-100), hedenbergite, tetrataenite, and awaruite.
Figure 6. Nuwaite (Ni6GeS2), a new secondary mineral in cracks with grossular in a Type B CAI from the Allende CV3 chondrite (Ma & Beckett, 2018). BSE image.
Figure 5. Davisite (CaScAlSiO6) and panguite [(Ti4+,Sc,Al,Mg,Zr,Ca)1.8O3] in an ultrarefractory inclusion within an amoeboid olivine inclusion from the Allende CV3 chondrite (Ma, Tshauner, Beckett, Rossman, & Liu, 2012). BSE image.
CK Chondrites
The CK group lacks highly unequilibrated members; petrologic types range from ~3.6 to 6. The principal primary phases in chondrules include olivine and low-Ca pyroxene; those in AOIs include olivine, anorthite, and diopside; those in CAIs include olivine, fassaite, and anorthite. Rare troilite and very rare kamacite also occur. Secondary phases in CK chondrites include magnetite, pentlandite, pleonaste, Ca-pyroxene, ilmenite, pyrite, Ni-bearing pyrrhotite, chalcopyrite, monosulfide solid solution, millerite, and tiny rare grains of noble-metal-rich sulfides, tellurides, and arsenides.
CR Chondrites
Primary phases in CR chondrules include olivine, low-Ca pyroxene, metallic Fe-Ni (kamacite and some martensite), troilite, and feldspathic glass; free silica occurs within igneous rims around many chondrules. Primary minerals in CAIs include melilite, Ca-pyroxene, spinel, hibonite, and grossite; rare ultrarefractory inclusions include Zr-rich and Sc-rich clinopyroxene. Matrix regions in the least-altered CR chondrites contain amorphous ferroan silicate grains associated with tiny particles of troilite and Fe-Ni sulfide. The metallic Fe-Ni grains in CR whole rocks have a solar Ni/Co ratio and exhibit a positive correlation between their Ni and Co contents. Secondary phases in CR chondrites include Fe-Mg serpentines, saponite, calcite, magnetite, pyrrhotite, pentlandite, iron-oxide, and rare tetrataenite. In the CR2.0 chondrite GRO 95577, there are chondrule pseudomorphs (aqueously altered chondrules) containing opaque assemblages consisting of kamacite cores surrounded by iron-oxide rinds. One such rind surrounds a core compositionally equivalent to a mixture enriched in iron carbonate (siderite) and ferrous sulfate.
CH Chondrites
These rocks are breccias consisting of chondrules, CAIs, abundant opaque phases, and a few volume percent type-1 carbonaceous-chondrite clasts and reduced clasts. Chondrules contain major forsterite, enstatite, glass, rare spinel, ferroan chromian spinel, ferroan olivine, and ferroan low-Ca pyroxene. Non-chondrule regions of the host contain abundant metallic Fe-Ni (major kamacite, minor plessite, and accessory taenite and tetrataenite), accessory sulfide (mainly Ni- and Cr-bearing troilite along with rare pentlandite and heazlewoodite), accessory oxide (spinel, ferroan chromian spinel, and magnetite). As in CR chondrites, the metallic Fe-Ni grains in CH chondrites exhibit a positive correlation between their Ni and Co contents; they also have a solar Ni/Co ratio. The principal phases in CAIs are hibonite, grossite, spinel, perovskite, melilite, and Al-rich diopside; some hibonite-rich, melilite-free inclusions contain glass. The most common type of C1 clast consists of magnetite (framboids—with the bumpy appearance of a raspberry, spherulites—small rounded bodies, platelets, and isolated grains), pentlandite, merrillite, troilite, olivine, dolomite, and phyllosilicates. The reduced clasts contain blebs of kamacite; adjacent silicate grains exhibit reduction halos.
CB Chondrites (Bencubbin-Type)
The coarse-grained CBa chondrites, such as Bencubbin and Gujba, contain: (a) abundant metallic Fe-Ni (present mainly as centimeter-size ellipsoidal nodules with minor to accessory troilite), (b) abundant light-colored silicate nodules with cryptocrystalline, barred pyroxene or barred olivine textures (consisting of magnesian monoclinic and orthorhombic low-Ca pyroxene, magnesian olivine, feldspathic glass, and rare Ca-pyroxene), (c) rare refractory inclusions (with spinel, Al-Ti diopside, and melilite), (d) rare matrix material consisting of silicate glass and fused droplets of metallic Fe-Ni, and (e) some high-pressure phases formed by shock (majorite, wadsleyite, coesite, grossular-pyrope, possibly majorite‐pyropess, and a variety of C-rich phases, including graphite, amorphous to poorly graphitized carbon, diamond, and bucky-diamond). Also present are amorphous carbonaceous nanoglobules. Not every CBa chondrite contains all these components.
The finer-grained CBb chondrites such as Hammadah al Hamra 237 and QUE 94411 contain: (a) very abundant metallic Fe-Ni (including chemically zoned individual grains), (b) common refractory inclusions (with spinel, hibonite, melilite, Al-Ti diopside, and forsterite), and (c) hydrated lithic clasts containing magnetite framboids and platelets, prismatic sulfide (pentlandite and pyrrhotite), complex Fe-Mn-Mg-Ca carbonates, and phyllosilicate (serpentine and saponite).
Enstatite Chondrites
The silicate phases in enstatite chondrites include monoclinic and orthorhombic low-Ca pyroxene, forsterite (in type-3 samples), calcic pyroxene, plagioclase, silica (cristobalite, quartz and tridymite), roedderite, and glass; a few shocked samples contain fluor-richterite or fluor-phlogopite. Fine-grained coesite occurs within a narrow shock vein in EH3 Asuka 10164. Enstatite-chondrite sulfides include troilite, niningerite, keilite, ferroan alabandite and alabandite, daubréelite, oldhamite, djerfisherite, caswellsilverite, and rare heideite, wassonite, sphalerite, and Mn-bearing pentlandite. Metallic Fe (nearly exclusively Si-bearing kamacite) is abundant; a few metallic Fe grains with ~8–11 wt.% Ni also occur. Lawrencite (FeCl2) is present as thin rims around silica grains, as inclusions within kamacite and troilite, and as isolated matrix grains in the EH4 Indarch fall. Also occurring in enstatite chondrites are silicides (i.e., perryite, in type-3 samples), nitrides (osbornite, nierite) (Figure 7), oxynitrides (sinoite), phosphides (schreibersite), carbides (cohenite), graphite, and shock-produced diamonds twinned on {111}. Rare CAIs contain spinel, hibonite and perovskite.
Figure 7. Euhedral nierite (Si3N4) grains from the Qingzhen EH3 enstatite chondrite. BSE image.
There are two separate groups of enstatite chondrites: EH (high iron) and EL (low iron). Both groups have members spanning the full range of petrologic types (3–6). They differ somewhat in mineralogy: EH chondrites contain niningerite; in many shocked EH chondrites, the niningerite has been converted to keilite. EL chondrites contain ferroan alabandite (in some cases alabandite) instead of niningerite. Only very rare grains of ferroan alabandite have been reported in shocked EH chondrites.
The most noticeable difference between EH and EL chondrites in oxidation state is in the concentration of Si in kamacite. It is higher in EH than EL chondrites, but generally increases with petrologic type in both groups: ~2 wt.% Si in EH3 kamacite, 2.6–3.5 wt.% Si in EH4 kamacite, ~4 wt.% Si in EH6 kamacite; and ~0.3–0.5 wt.% Si in EL3 kamacite, 0.9–1.8 wt.% Si in EL5 kamacite, 1.1–1.7 wt.% Si in EL6 kamacite.
Kakangari-Like Chondrites
In mid 2020, the Kakangari grouplet had four members: Kakangari (K3), LEW 87232 (K3), Lea County 002 (K3), and NWA 10085 (K4). Most chondrules are porphyritic (Type I) and contain more pyroxene than olivine; BO chondrules (chondrules containing bars of olivine (Mg,Fe)2SiO4) are present; other chondrule textural types are very rare or absent. Chondrule olivine and pyroxene grains are MgO-rich, for example, Kakangari olivine averages Fa2.2 and low-Ca pyroxene averages Fs4.4. Pyroxene is present as clinoenstatite, Ca-pyroxene (Wo30-50; containing 30–50 mol% of the wollastonite (CaSiO3) component), and pigeonite. In addition to olivine and pyroxene, Kakangari chondrules contain feldspathic mesostasis, silica, phosphate, metallic Fe-Ni, and troilite.
Refractory inclusions in Kakangari tend to be spinel-rich; some contain small grains of perovskite. These inclusions are rimmed by sodalite and Al-rich diopside. One reported hibonite-rich inclusion is rimmed by Cr-Al spinel, sodalite, and Al-rich diopside. A fassaite-rich inclusion with minor olivine has been described. Also present in Kakangari are AOIs, some of which contain fassaite rimmed by spinel.
The fine-grained component of matrix material in K3 chondrites consists of major enstatite (disordered intergrowths of ortho and clino), major forsterite and minor albite, anorthite, Cr-spinel, troilite, metallic Fe-Ni, and ferrihydrite. Coarse metallic Fe-Ni grains include kamacite (5–8 wt.% Ni, 0.2–0.5 wt.% Co) and taenite (24–34 wt.% Ni). The matrix in K4 NWA 10085 appears coarser and moderately recrystallized; mafic silicates in the matrix are compositionally uniform (Fa2.8-3.2; Fs3.6-4.5) and identical to those in chondrules.
Primitive Achondrites
Ureilites
Ureilites are carbon-bearing, ultramafic, olivine-pyroxene achondrites. Their olivine/(olivine+pyroxene) modal ratios vary widely from 0.1 to 1.0, although in most samples, olivine is more abundant than pyroxene. The total modal abundance of olivine+pyroxene is typically 80–90 vol.%. Most ureilites are highly equilibrated rocks with a mean olivine endmember composition somewhere in the range of Fa5-25, with a significant peak at Fa21; the dominant pyroxene phase is uninverted pigeonite with high Cr2O3 (up to 1.26 wt.%) and a mean endmember composition somewhere in the range of Fs8-20Wo5-11. Some ureilites contain pyroxene grains with clinopyroxene lamellae; in different samples, the lamellae range in thickness from ~0.01 µm (LEW 85440) to ~50 µm (LEW 88774).
Olivine grain cores have high concentrations of CaO (~0.30–0.45 wt.%) and Cr2O3 (~0.56–0.85 wt.%) and have FeO/MnO ratios of ~17–53. Olivine grains in contact with carbonaceous matrix material have 10–100 µm-thick reduced rims consisting of forsterite with abundant blebs of low-Ni kamacite. Reduced rims also occur on pyroxene grains (where they consist of enstatite and low-Ni kamacite) and, in LEW 88774, on chromite grains (where they consist primarily of Cr-rich cohenite, brezinaite—Cr3S4 and eskolaite—Cr2O3). In some ureilites, the olivine and pyroxene grains contain small opaque spherules consisting mainly of C-bearing metallic Fe-Ni, cohenite and troilite.
The most abundant phase in the C-rich matrix material between coarse silicate grains is graphite. In addition to graphite, some shocked ureilites contain variable amounts of chaoite, diamond and/or organic carbon.
Interstitial phases that occur in at least some ureilites include metallic Fe-Ni (with up to ~3 wt.% Si, ~1.5 wt.% Cr, and ~1 wt.% P), schreibersite, troilite, brezinaite, low-Ca pyroxene, augite, Al-Ti diopside, silica, Si-Al-alkali glass, chromite, and corundum.
Polymict ureilites contain clasts of monomict ureilites along with other lithic clasts (e.g., porphyritic enstatite, enstatite-granular-olivine, basaltic, angritic, phosphate-bearing feldspathic melt-rock, carbonaceous-chondritic matrix). Also present are a variety of interstitial phases including carbon, suessite, sulfide, chromite, apatite, halite, and sylvite. Plagioclase in the lithic clasts is highly variable, ranging in composition from An0-100, that is, 0–100 mol% of the anorthite (CaAl2Si2O8) component of the mineral plagioclase. Grains of intermediate composition (An30-80) tend to be free of K2O. Carbonaceous-chondrite-matrix-like clasts in Nilpena consist of saponite, serpentine, magnetite, pentlandite, pyrrhotite, and ferrihydrite.
Brachinites
Brachinites consist (in vol.%) of 74–98% olivine, 4–15% Ca-pyroxene (Cr-diopside or Cr-augite), 0.5–2% chromite, 3–7% Fe-sulfide (mainly Ni-bearing troilite, but Brachina also contains pentlandite), minor phosphate (mainly chlorapatite, but Hughes 026 also contains merrillite), minor Ni-rich metal (taenite and tetrataenite), 0–10% plagioclase, and, in some cases, accessory orthopyroxene. Olivine generally forms equigranular textures; interstitial phases include augite, chromite, and (where present) plagioclase.
Although individual brachinites contain homogeneous unzoned olivine, the overall compositional range is Fa30-35. Olivine has low Cr2O3 (0.01–0.08 wt.%), moderate MnO (0.3–0.6 wt.%), and moderate CaO (0.05–0.27 wt.%).
Acapulcoites and Lodranites
These two related groups have OC-like mineralogy and consist of orthopyroxene, olivine, Cr-diopside, sodic plagioclase, metallic Fe-Ni (kamacite and taenite), phosphide (schreibersite and melliniite), troilite, merrillite, chlorapatite, chromite, graphite, and rare metallic Cu (in acapulcoite Dhofar 1222). Acapulcoites are fine-grained rocks (150–230 μm); several contain a few volume percent (up to 6 vol.%) relict barred olivine (BO), radial pyroxene (RP), granular olivine-pyroxene (GOP), porphyritic pyroxene (PP), porphyritic olivine (PO), and porphyritic olivine-pyroxene (POP) chondrules. Lodranites are appreciably coarser grained (540–700 μm) and chondrule free.
Acapulcoites and lodranites have similar compositional ranges in olivine (Fa4.2-14.5, Fa3.1-13.7) and orthopyroxene (Fs3.3-13.3, i.e., 3.3–13.3 mol% of the ferrosilite (FeSiO3) component of low-Ca pyroxene (Fs3.7-13.8)). Many chondrule-free acapulcoites have Ca-pyroxene grains with thin exsolution lamellae. Lodranites contain inverted pigeonite grains with coarse Ca-pyroxene exsolution lamellae.
In volume percent, acapulcoites contain ~74–89% silicates, ~4–18% kamacite, 0–0.3% taenite, 2.7–6.4% troilite, 0–1.7% chromite, and ≤0.1% graphite; lodranites contain ~65–94% silicates, ~1–28% kamacite, 0–0.1% taenite, 0.1–3.1% troilite, 0–0.7% chromite, and ≤1.3% graphite.
Winonaites and IAB-Complex Silicates
Winonaites and IAB-Complex irons were probably derived from the same parent asteroid; individual winonaites could be large IAB silicate inclusions freed from their iron-meteorite hosts. Most winonaites are fine-to-medium-grained equigranular rocks with OC-like minerals, plus a few reduced phases. These rocks consist of (in vol.%): 15–30% forsterite (Fo95-100) (i.e., 95–100 mol% of the forsterite (Mg2SiO4) component of olivine), 25–45% orthopyroxene (En91-100) (i.e., 91–100 mol% of the enstatite (MgSiO3) component of low-Ca pyroxene), 1–7% Cr-diopside, 6–14% sodic plagioclase (An7-25), 0.1–13% metallic Fe-Ni, 1–19% troilite, 0–0.6% graphite, 0–1% schreibersite, 0–0.2% chromite and accessory phosphate (merrillite), daubréelite, and alabandite. Mineral compositions are more reduced than those in H chondrites. One of the most primitive winonaites is NWA 1463. It contains abundant, readily identifiable relict chondrules.
Hammadah al Hamra 193 is an unusual winonaite consisting mainly of large orthopyroxene grains enclosing olivine and plagioclase. It contains fluorapatite (instead of merrillite) and large grains of the amphibole fluoro-edenite enclosing Ca-pyroxene, orthopyroxene, plagioclase, and olivine. The texture of HaH 193 suggests that fluoro-edenite formed from diopside, olivine, and plagioclase, and replaced clinopyroxene.
IAB-Complex irons include meteorites with silicate inclusions similar in mineralogy to those in winonaites. The most common phases in silicate inclusions are forsterite, enstatite, Cr-diopside, sodic plagioclase, phosphate (mainly chlorapatite and merrillite), chromite, magnesiochromite, metallic Fe-Ni, troilite, schreibersite, and graphite. Rare phases include cohenite, alabandite, ferroan alabandite, daubréelite, sphalerite, metallic Cu, and K-feldspar. San Cristobal inclusions contain antiperthite (exsolution lamellae of K-feldspar within sodic plagioclase), roedderite, haxonite, and brianite. Campo del Cielo contains 0.4–1.3 mm-size recrystallized POP chondrules consisting of magnesian olivine and orthopyroxene, Ca-pyroxene, albitic plagioclase and minor pyrrhotite, chromite, and, in one case, rutile.
Carlton and Dayton are Ni-rich IAB Complex irons, previously designated IIICD. Many of their silicate inclusions are rich in phosphate. Carlton inclusions contain abundant chlorapatite and farringtonite-brianite; one inclusion has a single 175 × 975 μm grain of chladniite in association with olivine, orthopyroxene, sodic plagioclase, schreibersite, and troilite. Dayton inclusions lack olivine, graphite, and carbide, but contain free silica along with brianite and panethite.
Asteroidal Achondrites
Howardites, Eucrites, and Diogenites
Most members of these three related groups were probably derived from the same parent asteroid, widely assumed to be 4 Vesta.
Eucrites are igneous volcanic monomict breccias or unbrecciated rocks rich in pyroxene (with <10 vol.% orthopyroxene) and calcic plagioclase. Ordinary non-cumulate eucrites were significantly metamorphosed; they contain pigeonite (initially Fs48-58Wo6-15) with fine augite exsolution lamellae parallel to (001) and compositionally zoned plagioclase grains (e.g., An80-93 in Juvinas). Lava-like eucrites were mildly metamorphosed; they contain zoned pigeonite (Fs30-80), zoned plagioclase, and minor ilmenite. Cumulate eucrites are coarse-grained gabbros: Binda-type samples contain orthopyroxene with blebby augite, and inverted low-Ca clinopyroxene (initially Fs32-46Wo7-16); Moore County-type samples contain orthopyroxene, inverted pigeonite with thick augite exsolution lamellae parallel to (001), and compositionally unzoned plagioclase (in the range An90-98). Polymict eucrites are breccias with <10 vol.% primary orthopyroxene. Minor and accessory phases present in some eucrites include olivine, silica (tridymite and quartz), ilmenite, chromite, phosphate (merrillite and apatite), low-Ni kamacite, troilite, zircon, and baddeleyite. A few polymict eucrites contain pyroxferroite; troilite, hedenbergite, and silica are present in NWA 1109.
Diogenites are orthopyroxenites (monomict breccias or unbrecciated rocks) with <10 vol.% plagioclase. They consist largely (~84–100 vol.%) of orthopyroxene (Fs15-33Wo1-2) with minor chromite; some contain major olivine or silica. Metallic Fe-Ni and troilite are present in minor-to-accessory amounts. A few diogenites have noritic lithologies and consist of significant orthopyroxene, Ca-plagioclase, and olivine, as well as minor pigeonite and augite. Diopside is present in some diogenites as exsolution products. Rare phosphate also occurs.
Howardites are polymict breccias composed predominantly of eucritic and diogenitic clasts. Some (e.g., Bholghati, Jodzie, Kapoeta, Y793497) also contain a few volume percent carbonaceous-chondrite clasts (~80% CM2, ~20% CR2), impact-melt-coated breccia clasts, and impact-melt rock clasts.
Angrites
Most angrites are medium-to-coarse-grained unbrecciated igneous rocks, mainly basalts, although Angra dos Reis (AdoR) itself is a granular olivine pyroxenite. All angrites are silica-undersaturated, alkali-depleted, and moderately Ca-and Ti-rich rocks with normative nepheline and larnite (La, Ca2SiO4). The AdoR fall (1.5 kg) contains 93 vol.% homogeneous Al-Ti-diopside (Fs12Wo55), minor Ca-bearing olivine (Fa46; 1.3 wt.% CaO), hercynite and troilite, and accessory Mg-kirschsteinite, celsian, merrillite, titanomagnetite, baddeleyite, and metallic Fe-Ni. There are also a few reports of plagioclase grains among mineral separates.
Other angrites contain 20–24 vol.% normally zoned Al-Ti diopside (with Fs21Wo53 cores and Fs48Wo52 rims), 29–42 vol.% normally zoned olivine, 33–36 vol.% Ca-plagioclase, accessory hercynite, spinel, Cr-pleonaste, ulvöspinel, titanomagnetite, glass, metallic Fe-Ni, troilite and merrillite, and rare carbonates, baddeleyite, celsian, and rhönite. Olivine phenocrysts have Fa10-27 cores, Fa55-100 rims and <0.1 wt.% CaO; euhedral groundmass olivines have Fa34 cores and Fa58La37 rims. LEW 86010 contains anorthitic plagioclase and homogeneous olivine (Fa63; 1.5-2.6 wt.% CaO) with kirschsteinite exsolution lamellae.
Aubrites (Enstatite Achondrites)
This achondrite group comprises highly reduced differentiated rocks with very little oxidized iron. Aubrites contain 75–98 vol.% enstatite (Fs0.06), 0.3–16 vol.% albite (Ab92.7Or3.2), 0.2–8 vol.% diopside (Fs0.08Wo43.5), 0.3–10 vol.% forsterite (Fa0.01), and minor-to-accessory amounts of a large variety of phases: metallic Fe-Ni (Si-bearing kamacite, Si-poor kamacite, Si-bearing taenite), numerous sulfides (Ti-bearing and Cr-bearing troilite, heideite, caswellsilverite, oldhamite, niningerite, djerfisherite, brezinaite, daubréelite, alabandite, ferromagnesian alabandite, sphalerite, Sb- and Ag-sulfides), graphite, silica (cristobalite, tridymite), roedderite, schreibersite, perryite, osbornite, metallic Cu, and feldspathic glass.
Aubritic enstatite is mainly disordered orthopyroxene, but clinoenstatite occurs in some microporphyritic clasts in Norton County. Exsolved diopside constitutes up to ~25 vol.% of host enstatite grains in some aubrites, indicating that these pyroxene grains are inverted pigeonite.
Most aubrites are breccias, mainly monomict fragmental breccias; a few are regolith breccias containing solar-wind-implanted rare gases. Cumberland Falls, ALH 78113, and Larned are polymict breccias. Numerous dark clasts in Cumberland Falls were derived from ordinary chondrites; the clasts have all been shocked, and some clasts are impact-melt breccias. The ordinary-chondrite clasts have been reduced: olivine is very magnesian (Fa0.4-0.7), low-Ca pyroxene grains are reversely zoned, and some reduced phases are present—daubréelite and schreibersite.
Mayo Belwa is an impact-melt breccia containing ~5 vol.% vugs; some vugs are lined with granular enstatite, acicular diopside, minor cristobalite, and bundles of albite laths. Other vugs are lined with bundles of acicular grains of fluor-richterite.
The unbrecciated aubrites Shallowater and Mount Egerton appear to be from a different asteroid than the majority of aubrites. These two rocks contain much more metallic Fe-Ni (8.4 and 21 wt.%, respectively) than average aubrites (~0.5 wt.%). The metal abundance in Mount Egerton is similar to the average in enstatite chondrites (~22 wt.%). Both Shallowater and Mount Egerton have bulk positive Eu anomalies, unlike most aubrites. These two meteorites also have near-identical cosmic-ray exposure ages (27.0 Ma and 26.9 Ma).
Phases produced from primary minerals in aubrites by terrestrial weathering include: (a) schöllhornite (Na0.3(H2O)CrS2), derived from caswellsilverite (NaCrS2), (b) portlandite (Ca(OH)2), vaterite (hexagonal CaCO3), calcite (trigonal CaCO3), bassanite (CaSO4∙½H2O), and barite (BaSO4), all likely derived from oldhamite (CaS), and (c) goethite (FeO(OH)), derived from metallic Fe-Ni.
Non-Asteroidal Achondrites
Lunar Meteorites
About 80% of lunar meteorites are broadly anorthositic or feldspathic. These rocks contain varying abundances of anorthite, olivine, orthopyroxene, clinopyroxene (pigeonite, ferropigeonite, diopside, augite, sub-calcic augite), silica, oxides (chromite, Ti-chromite, Cr-ulvöspinel, ilmenite, rutile, Cr-pleonaste, baddeleyite), K-bearing glass, and small amounts of kamacite and troilite.
About 15% of lunar meteorites are broadly basaltic or gabbroic. They contain major calcic plagioclase and clinopyroxene (augite, sub-calcic augite, pigeonite), accessory silica (probably tridymite), rare olivine, and trace amounts of metallic Fe-Ni and troilite. Some of these rocks contain additional phases, including hedenbergite, pyroxferroite, ilmenite, chromite, Ti-magnetite, and apatite.
About 5% of lunar meteorites are mixed, mingled, or polymict breccias. Their mineral constituents are a combination of those in anorthositic and basaltic samples.
Martian Meteorites
About 82% of martian meteorites are shergottites and related rocks containing (a) major pyroxene (augite, sub-calcic augite, pigeonite, and/or orthopyroxene), olivine (Fa24-40) and maskelynite, and/or plagioclase (Ab30-50), (b) minor oxides (magnetite, titanomagnetite, ulvöspinel, ilmenite, chromite, hercynite, baddeleyite), phosphates (merrillite, chlorapatite), and sulfide (pyrrhotite, pentlandite) and (c) some late-stage phases (silica, pyroxferroite, fayalite, hercynite, and ferro-kaersutite).
About 9% of martian meteorites are nakhlites with (a) major augite, sub-calcic augite, olivine, and mesostasis, and (b) minor to accessory pigeonite, orthopyroxene, plagioclase, K-feldspar, silica, titanomagnetite, ulvöspinel, rutile, magnetite, hercynite, chlorapatite, merrillite, pyrrhotite, pyrite, marcasite, and chalcopyrite.
About 1% of martian meteorites are chassignites. They consist of ≥90 vol.% olivine and minor to accessory orthopyroxene (Fs19Wo3), pigeonite, augite, plagioclase, sanidine, chromite, chlorapatite, troilite, pentlandite, ilmenite, rutile, baddeleyite, kaersutitic amphibole, biotite, and phlogopite.
The martian-meteorite suite also includes two pyroxenites—ALH 84001 (with major orthopyroxene and minor to accessory chromite, maskelynite, augite, apatite, pyrite, and carbonate) and NWA 2646 (with major pigeonite, augite, olivine and maskelynite and minor oxides, phosphate, and sulfide).
Martian meteorites also contain many high-pressure phases produced during launch off Mars: maskelynite, akimotoite, ahrensite, lingunite, majorite, ringwoodite, tuite, bridgmanite, wüstite-FeO, tissintite, xieite, chenmingite, zagamiite, and liebermannite (Figure 8).
Figure 8. Shock-induced, high-pressure minerals form the Tissint shergottite. (a) Ahrensite (Fe2SiO4-spinel), bridgmanite [(Mg,Fe)SiO3-perovskite], and wüstite [(Fe,Mg)O], formed from fayalite (Ma et al., 2016). (b) Tissintite [(Ca,Na,□)AlSi2O6], a clinopyroxene formed from maskelynite in a melt pocket (Ma et al., 2015). BSE images.
Iron Meteorites
The most common minerals in iron meteorites are metallic Fe-Ni (kamacite, martensite, taenite, tetrataenite), sulfide (troilite, daubréelite), phosphide (schreibersite), carbide (cohenite, haxonite, edscottite) (Figure 9), native carbon (graphite, diamond), native copper, nitride (carlsbergite), oxide (chromite, fusion-crust magnetite), and phosphate (merrillite, chlorapatite). Although Neumann-banded kamacite, martensite and ε-structured metal (a high-density hexagonal close-packed structure) are present in many specimens, these are shock products.
Figure 9. Edscottite (Fe5C2) in low-Ni iron, with taenite and nickelphosphide from the Ni-rich Wedderburn IAB iron meteorite (Ma & Rubin, 2019). BSE image.
The principal phases in silicate inclusions vary by iron-meteorite group. Many troilite nodules in IVB Tawallah Valley are surrounded by 10–20 µm-thick bands of swathing kamacite; a few troilite nodules in Santa Clara contain small (<25 µm) grains of silica. Some troilite nodules in IIAB Coahuila and Hex River Mountains contain 1–5 mm grains of kosmochlor and additional unidentified silicates. Puente del Zacate is unique in possessing a 7 mm angular silicate inclusion within a 16 mm-diameter troilite nodule. The silicate inclusion has a granoblastic texture and consists (in wt.%) of 23% olivine (Fa4), 14% low-Ca pyroxene (Fs6Wo1), 15% Cr-diopside (Fs3Wo47), 15% plagioclase (Ab82Or4), 1% troilite, 0.5% chromite, 0.5% daubréelite, 4% metallic Fe-Ni, and 27% graphite (or cavities that once contained graphite). Group IVA irons Gibeon and Bishop Canyon contain tabular tridymite. Steinbach and São João Nepomuceno (SJN) have clumps of coarse-grained low-Ca pyroxene (up to 3.5 mm long) and tridymite (up to 1 × 2.6 mm). Most of the low-Ca pyroxene in these two meteorites is orthobronzite (Steinbach: Fs14.5-15.5Or0.21-1.1(i.e., 0.21–1.1 mol% of the orthoclase (KAlSi3O8) component of plagioclase); SJN: Fs12.6-13.8Or0.45-0.57), the remainder is clinobronzite with polysynthetic twinning. About half of the orthopyroxene grains in SJN contain small inclusions of troilite, chromite, metallic Fe-Ni, or tridymite as isolated grains or in a variety of intergrowths; some of the orthopyroxene grains in Steinbach contain similar inclusions, but at lower modal abundances.
Silicate-rich inclusions in IAB irons occur commonly as millimeter-to-centimeter-size nodules. The principal phases in the silicate-rich inclusions are forsterite, enstatite, Cr-diopside, albite, chlorapatite, merrillite, chromite, metallic Fe-Ni, troilite, schreibersite, and graphite. Minor-to-accessory phases include cohenite, alabandite, daubréelite, sphalerite, and metallic Cu. Toluca contains kosmochlor. San Cristobal (unique IAB) contains K-feldspar with antiperthite exsolution lamellae, roedderite, haxonite, and brianite. Various phosphates (chlorapatite, farringtonite, brianite, panethite) are present in Carlton and Dayton. The abundance of silicate inclusions in IIE irons ranges from 0 to 15 vol.%. They are of two general types:
Unfractionated inclusions with chondritic bulk compositions are present in Netschaëvo, Techado and Watson 001. Netschaëvo contains angular chondrule-bearing clasts (surrounded by swathing kamacite) that have been recrystallized to petrologic type 6. Chondrule textural types include BO (barred olivine), PO (porphyritic olivine), PP (porphyritic pyroxene), POP (porphyritic olivine-pyroxene), and RP (radial pyroxene); constituent minerals include olivine, low-Ca pyroxene, Ca-pyroxene, plagioclase, merrillite, chlorapatite, chromite, troilite, schreibersite, and metallic Fe-Ni. Techado contains a roughly ellipsoidal inclusion with coarse grains of olivine, low-Ca pyroxene, and feldspar. Watson 001 has a 10 cm-long subrounded-to-subangular inclusion consisting of major coarse orthopyroxene with poikilitically enclosed olivine, Ca-pyroxene, and albite with antiperthite exsolution of alkali feldspar, as well as minor merrillite and chromite.
Fractionated inclusions tend to have globular shapes and contain little or no olivine (≲2 vol.%). They are rich in sodic feldspar (albite or oligoclase), Si-rich glass or tridymite, K-feldspar, antiperthite feldspar, and Ca-pyroxene. Minor-to-accessory phases include pigeonite, phosphate (merrillite and apatite—chlorapatite in many specimens, fluorapatite in Elga), oxide (ilmenite, rutile, armalcolite), pentlandite, and sodalite. Colomera contains an 11 cm-long sanidine crystal as well as yagiite—(K,Na)2(Mg,Al)5(Si,Al)12O30 and Ca-pyroxene.
Stony-Iron Meteorites
Pallasites
The principal primary minerals in pallasites include metallic Fe-Ni (kamacite, taenite, plessite), olivine, troilite, schreibersite, chromite, phosphate (farringtonite, stanfieldite, merrillite), low-Ca pyroxene (orthopyroxene, clinoenstatite-clinobronzite), and Ca-pyroxene (augite to diopside). Fukang contains silica/felsic inclusions with tridymite, K-rich glass, and an unidentified Ca-Cr silicate phase. (The latter phase also occurs in Pavlodar.) NWA 10019 and Choteau contain minor plagioclase. Vermillion contains cohenite; trace amounts of graphite were reported in Brenham and Krasnojarsk. Rare or trace phases include (a) pentlandite in Newport (although pentlandite in most pallasites is secondary), (b) mackinawite in Dora, Imilac, Itzawisis and Thiel Mountains, (c) metallic Cu in Brenham, Glorieta Mountain, Lipovsky, Molong, and Newport, and (d) rutile in Rawlinna 001.
Two meteorites are commonly called “pyroxene pallasites.” Vermillion contains 86 vol.% metallic Fe-Ni (kamacite, taenite, and small amounts of schreibersite, troilite and cohenite) and 14 vol.% silicates. The silicate portion consists (in vol.%) of 93% olivine (Fa11.1-13.0), 4.9% orthopyroxene (averaging Fs10.7Wo1.7), 0.1% Ca-pyroxene (averaging Fs4.8Wo44.2), 1.5% chromite (present as euhedral-to-rounded grains within metal), and 0.5% merrillite.
Y-8451 contains 43 vol.% metallic Fe-Ni (taenite, plessite, and kamacite, as well as small amounts of troilite and schreibersite) and 57 vol.% silicates. The silicate portion consists (in vol.%) of 97% olivine (Fa10.2-11.2), 2.0% polysynthetically twinned low-Ca clinopyroxene (averaging Fs9.5Wo0.6), 0.4% untwinned orthopyroxene (averaging Fs10.0Wo1.9), 0.4% Ca-pyroxene (Fs4.0Wo44.1), 0.1% merrillite, and trace amounts of submicrometer-size chromite grains within symplectic intergrowths with augite.
Mesosiderites
Mesosiderites are an enigmatic group of stony-iron breccias averaging roughly 50 wt.% metallic Fe-Ni, troilite, and schreibersite (with an actual range of 18–90 wt.% metal, 0.6–14 wt.% troilite, and 0–0.1 wt.% schreibersite) and roughly 50 wt.% silicate (with a range of 28–80 wt.%). Silicate phases include major orthopyroxene and plagioclase and minor Ca-pyroxene, olivine, and tridymite. Also present are minor-to-trace amounts of merrillite, chromite, and ilmenite.
There are three compositional classes of mesosiderites:
Class-A samples are basaltic and relatively rich in plagioclase and Ca-pyroxene; they contain (in vol.%): 55 ± 5% orthopyroxene, 29 ± 8% plagioclase, and 6 ± 2% tridymite.
Class-B samples are more ultramafic and relatively rich in orthopyroxene; they contain (in vol.%): 76 ± 5% orthopyroxene, 17 ± 4% plagioclase, and 2 ± 2% tridymite.
Class C, represented by RKPA79015, has very abundant orthopyroxene. One silicate-rich region was found to contain 67.2 vol.% orthopyroxene, only 0.2 vol.% silica, and no plagioclase or olivine. Additional phases in this region include 8.5 vol.% metal, 23.2 vol.% troilite, 0.1 vol.% schreibersite, 0.6 vol.% merrillite, and 0.2 vol.% chromite.
Conclusions
About 470 minerals have been identified in meteorites by mid 2020. The number is large because meteorites are derived from many different bodies, each with a distinctive geochemical character. Meteorites are now thought to come from 100–150 asteroids, as well as from the Moon and Mars. In addition, primitive chondrites contain tiny presolar grains that formed in the outflows of evolved stars and as supernova ejecta. These particles probably predate the solar system by hundreds of millions of years.
The vast majority of meteoritic minerals also occur in terrestrial rocks, but quite a few are rare or absent on Earth. For example, some refractory meteoritic minerals within CAIs (e.g., hibonite, perovskite, PGE-dominated alloys) can be found only as rare phases in metamorphosed limestones (hibonite), nepheline syenites and carbonatites (perovskite), and assorted ultramafic rocks (PGE-dominated alloys). Some refractory CAI minerals (e.g., davisite, warkite, rubinite, machiite, addibischoffite, grossite, panguite, kangite) do not occur on Earth. Other meteoritic minerals that are absent from terrestrial rocks are products of shock metamorphism (e.g., ahrensite, akimotoite, zagamiite, chenmingite, tuite). Some exclusively meteoritic phases form by terrestrial weathering of primary non-terrestrial minerals (e.g., schöllhornite from oldhamite). Meteoritic sulfides formed under highly reducing conditions (e.g., oldhamite, wassonite, heideite, djerfisherite, caswellsilverite, niningerite, keilite) also are not found in terrestrial rocks.
Some well-known terrestrial minerals have not been identified in meteorites. Some of these phases contain rare elements as major components (e.g., beryl—Be3Al2Si6O18; stibnite—Sb2S3; borax—Na2B4O5·8H2O); without improbable concentration mechanisms, such species would not be expected on asteroids. Other terrestrial minerals are composed of abundant elements, but form under conditions of high static pressure and temperature unlikely to occur on asteroids (e.g., the Al2SiO5 polymorphs—kyanite, sillimanite, and andalusite). Nevertheless, it is conceivable that these phases could be present on other planetary bodies and arrive on Earth within meteorites.
New meteoritic minerals are being discovered at an accelerated rate. This is due to the development and continual improvement of analytical techniques down to micro- and nano-scales (e.g., X-ray diffraction, electron probe microanalysis, scanning electron microscopy, and transmission electron microscopy), the recovery of tens of thousands of meteorites from hot and cold deserts, and a sharp increase in the number of meteorite researchers.
Acknowledgments
A version of this article is expected to appear in the book Meteorite Mineralogy by Alan Rubin and Chi Ma, to be published by Cambridge University Press in 2021.
Further Reading
- Bradley, J. P. (2005). Interplanetary dust particles. In A. M. Davis (Ed.), Meteorites, comets, and planets; Treatise on Geochemistry (Vol. 1, pp. 689–711). Amsterdam, The Netherlands: Elsevier.
- Brearley, A. J. (2006). The action of water. In D. S. Lauretta & H. Y. McSween (Eds.), Meteorites and the early solar system II (pp. 587–624). Tucson: University of Arizona Press.
- Buchwald, V. F. (1975). Handbook of iron meteorites. Berkeley, California: University of California Press.
- Buseck, P. R. (1977). Pallasite meteorites—Mineralogy, petrology and geochemistry. Geochimica et Cosmochimica Acta, 41(6), 711–740.
- El Goresy, A. (1976). Opaque oxide minerals in meteorites. In D. Rumble (Ed.), Oxide Minerals (pp. EG47–EG72). Blacksburg, VA: Mineralogical Society of America.
- Frondel, J. W. (1975). Lunar mineralogy. New York, NY: Wiley.
- Geiger, T., & Bischoff, A. (1995). Formation of opaque minerals in CK chondrites. Planetary and Space Science, 43(3-4), 485–498.
- Grossman, J. N., & Brearley, A. J. (2005). The onset of metamorphism in ordinary and carbonaceous chondrites. Meteoritics & Planetary Science, 40(1), 87–122.
- Hutchison, R. (2004). Meteorites: A petrologic, chemical and isotopic synthesis. Cambridge, UK: Cambridge University Press.
- Kerridge, J. F., & Matthews, M. S. (1988). Meteorites and the early solar system. Tucson: University of Arizona Press.
- Krot, A. N. (2019). Refractory inclusions in carbonaceous chondrites: Records of early solar system processes. Meteoritics & Planetary Science, 54(8), 1647–1691.
- Mittlefehldt, D. W., McCoy, T. J., Goodrich, C. A., & Kracher, A. (1998). Non-chondritic meteorites from asteroidal bodies. In J. J. Papike (Ed.), Planetary materials (pp. 4–1 and 4–195). Reviews in Mineralogy, 36. Washington, DC: Mineralogical Society of America.
- Olsen, E., Huebner, J. S., Douglas, J. A. V., & Plant, A. G. (1973) Meteoritic amphiboles. American Mineralogist, 58(9-10), 869–872.
- Ramdohr, P. (1973). The opaque minerals in stony meteorites. Amsterdam, The Netherlands: Elsevier.
- Rubin, A. E., & Ma, C. (2017). Meteoritic minerals and their origins. Chemie der Erde—Geochemistry, 77(3), 325–385.
- Scott, E. R. D. (2007). Chondrites and the protoplanetary disk. Annual Review of Earth and Planetary Science, 35, 577–620.
- Simon, S. B., & Grossman, L. (1992). Low-temperature exsolution in refractory siderophile element-rich opaque assemblages from the Leoville carbonaceous chondrite. Earth and Planetary Science Letters, 110(1-4), 67–75.
- Smith, J. V., & Steele, I. M. (1976). Lunar mineralogy: A heavenly detective story. Part II. American Mineralogist, 61(11-12), 1059–1116.
- Stöffler, D., Keil, K., & Scott, E. R. D. (1991). Shock metamorphism of ordinary chondrites. Geochimica et Cosmochimica Acta, 55(12), 3845–3867.
- Tomioka, N., & Miyahara, M. (2017). High-pressure minerals in shocked meteorites. Meteoritics & Planetary Science, 52(9), 2017–2039.
- Treiman, A. H. (2005). The nakhlite meteorites: Augite-rich igneous rocks from Mars. Chemie der Erde—Geochemistry, 65(3), 203–270.
- Weisberg, M. K., & Kimura, M. (2012). The unequilibrated enstatite chondrites. Chemie der Erde—Geochemistry, 72(2), 101–115.
- Zinner, E. K. (2005). Presolar grains. In A. M. Davis (Ed.), Meteorites, comets, and planets (pp. 17–39). Oxford, UK: Elsevier.
- Zolensky, M. E., & McSween, H. Y. (1988). Aqueous alteration. In J. F. Kerridge & M. S. Matthews (Eds.), Meteorites and the early solar system (pp. 114–143). Tucson: University of Arizona Press.
References
- Krot, A. N., Nagashima, K., & Rossman, G. R. (2020). Machiite, Al2Ti3O9, a new oxide mineral from the Murchison carbonaceous chondrite: A new ultrarefractory phase from the solar nebula. American Mineralogist, 105(2), 239–243.
- Ma, C., & Beckett, J. R. (2018). Nuwaite (Ni6GeS2) and butianite (Ni6SnS2), two new minerals from the Allende meteorite: Alteration products in the early solar system. American Mineralogist, 103(12), 1918–1924.
- Ma, C., & Rubin, A. E. (2019). Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite. American Mineralogist, 104(9), 1351–1355.
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Appendix
Alphabetical List of Meteoritic Minerals |
|
|---|---|
addibischoffite |
Ca2Al6Al6O20 |
adrianite |
Ca12(Al4Mg3Si7)O32Cl6 |
aenigmatite |
Na2Fe2+5TiSi6O20 |
ahrensite |
Fe2SiO4 |
akaganéite |
Fe3+O(OH,Cl) |
åkermanite |
Ca2MgSi2O7 |
akimotoite |
(Mg,Fe)SiO3 |
alabandite |
MnS |
albite |
NaAlSi3O8 |
albitic jadeite |
(Na,Ca,□1/4)(Al,Si)Si2O6 |
allabogdanite |
(Fe,Ni)2P |
allendeite |
Sc4Zr3O12 |
almandine |
Fe3Al2(SiO4)3 |
altaite |
PbTe |
Al-Ti diopside |
Ca(Mg,Ti,Al)(Si,Al)2O6 |
aluminum |
Al |
amakinite |
(Fe,Mg)(OH)2 |
amesite |
Mg2Al(SiAl)O5(OH)4 |
anatase |
TiO2 |
andradite |
Ca3Fe2(SiO4)3 |
andreyivanovite |
FeCrP |
anhydrite |
CaSO4 |
ankerite |
Ca(Fe2+,Mg,Mn)(CO3)2 |
anorthite |
CaAl2Si2O8 |
anosovite (not approved) |
(Ti4+,Ti3+,Mg,Sc,Al)3O5 |
anthophyllite |
(Mg,Fe)7Si8O22(OH)2 |
antigorite |
Mg3Si2O5(OH)4 |
antitaenite (not approved) |
Fe3Ni |
apatite |
Ca5(PO4)3(F,OH,Cl) |
aragonite |
CaCO3 |
armalcolite |
(Mg,Fe)Ti2O5 |
arupite |
Ni3(PO4)2·8H2O |
asimowite |
Fe2SiO4 |
aspidolite |
NaMg3(Si3Al)O10(OH)2 |
augite |
Mg(Fe,Ca)Si2O6 |
awaruite |
Ni3Fe |
baddeleyite |
ZrO2 |
baghdadite |
Ca3(Zr,Ti)Si2O9 |
baryte |
BaSO4 |
barringerite |
(Fe,Ni)2P |
barringtonite |
MgCO3·2H2O |
barroisite |
☐NaCa(Mg3Al2)(Si7Al)O22(OH)2 |
bassanite |
CaSO4·½H2O |
beckettite |
Ca2V6Al6O20 |
berthierine |
(Fe2+,Fe3+,Mg)3(Si,Al)2O5(OH)4 |
beusite |
(Mn,Fe,Ca,Mg)3(PO4)2 |
biotite |
K(Mg,Fe)3(Si3Al)O10(OH,F)2 |
bismuth chloride (not approved) |
BiCl3 |
blödite |
Na2Mg(SO4)2·4H2O |
böhmite |
AlO(OH) |
bornite |
Cu5FeS4 |
breunnerite |
(Mg,Fe)CO3 |
brezinaite |
Cr3S4 |
brianite |
Na2CaMg(PO4)2 |
bridgmanite |
MgSiO3 |
britholite-(Ce) |
(Ce,Y,Ca)5(SiO4,PO4)3(OH,F) |
browneite |
MnS |
brownleeite |
MnSi |
brucite |
Mg(OH)2 |
β-silicon nitride (not approved) |
β-Si3N4 |
buchwaldite |
NaCaPO4 |
bunsenite |
NiO |
burnettite |
CaV3+AlSiO6 |
buseckite |
(Fe,Zn,Mn)S |
butianite |
Ni6SnS2 |
Ca-armalcolite (not approved) |
CaTi2O5 |
calcite |
CaCO3 |
calzirtite |
Ca2Zr5Ti2O16 |
carbonate-fluorapatite |
Ca5(PO4,CO3)3F |
carletonmooreite |
Ni3Si |
carlsbergite |
CrN |
cassidyite |
Ca2(Ni,Mg)(PO4)2·2H2O |
caswellsilverite |
NaCrS2 |
celestine |
SrSO4 |
celsian |
BaAl2Si2O8 |
chabazite-Na |
(Na3K)Al4Si8O24·11H2O |
chalcocite |
Cu2S |
chalcopyrite |
CuFeS2 |
chamosite |
(Fe2+,Mg,Al,Fe3+)6(Si,Al)4O10(OH,O)8 |
chaoite |
C |
chenmingite |
FeCr2O4 |
chevkinite-(Ce) |
(Ce,Nd,La,Ca,Th)4(Ti,Fe,Mg)5Si4O22 |
chladniite |
Na2CaMg7(PO4)6 |
chlorapatite |
Ca5(PO4)3Cl |
chlormagaluminite |
Mg4Al2(OH)12Cl2·3H2O |
chlormayenite |
Ca12Al14O32Cl2 |
chopinite |
Mg3(PO4)2 |
chromite |
FeCr2O4 |
chrysotile |
Mg3Si2O5(OH)4 |
chukanovite |
Fe2(CO3)(OH)2 |
cinnabar |
HgS |
clinochlore |
(Mg,Fe2+)5Al(Si3Al)O10(OH)8 |
clinoenstatite |
Mg2Si2O6 |
clintonite |
Ca(Mg,Al)3(Al,Si)4O10(OH,F)2 |
cobaltite |
CoAsS |
coesite |
SiO2 |
cohenite |
(Fe,Ni)3C |
collinsite |
Ca2(Mg,Fe,Ni)(PO4)2·2H2O |
cooperite |
PtS |
copiapite |
Fe5(SO4)6(OH)2·20H2O |
copper |
Cu |
coquimbite |
Fe2(SO4)3·9H2O |
cordierite |
Mg2Al4Si5O18 |
corundum |
Al2O3 |
coulsonite |
FeV2O4 |
covellite |
CuS |
cristobalite |
SiO2 |
cronstedtite |
(Fe2+,Fe3+)3(Si,Fe3+)2O5(OH)4 |
cronusite |
Ca0.2CrS2·2H2O |
Cu-Cr-sulfide (not approved) |
CuCrS2 |
cubanite |
CuFe2S3 |
cupalite |
CuAl |
cuprite |
Cu2O |
czochralskiite |
Na4Ca3Mg(PO4)4 |
daubréelite |
FeCr2S4 |
davisite |
CaScAlSiO6 |
decagonite |
Al71Ni24Fe5 |
diamond |
C |
digenite |
Cu1.8S |
diopside |
CaMgSi2O6 |
djerfisherite |
K6(Fe,Cu)25S26Cl |
dmisteinbergite |
CaAl2Si2O8 |
dmitryivanovite |
CaAl2O4 |
dolomite |
CaMg(CO3)2 |
donpeacorite |
(Mn,Mg)Mg(SiO3)2 |
donwilhelmsite |
CaAl4Si2O11 |
droninoite |
Ni6Fe3+2Cl2(OH)16·4H2O |
edenite |
NaCa2Mg5Si7AlO22(OH)2 |
edscottite |
Fe5C2 |
electrum (not approved) |
Au-Ag |
enstatite |
Mg2Si2O6 |
epsomite |
MgSO4·7H2O |
eringaite |
Ca3Sc2Si3O12 |
erlichmanite |
OsS2 |
eskolaite |
Cr2O3 |
farringtonite |
Mg3(PO4)2 |
fayalite |
Fe2SiO4 |
feiite |
Fe2+2(Fe2+Ti4+)O5 |
feldspar group |
(K,Na,Ca)(Si,Al)4O8 |
feroxyhyte |
Fe3+O(OH) |
ferrihydrite |
Fe3+10O14(OH)2 |
ferroan alabandite |
(Mn,Fe)S |
ferroan antigorite |
(Mg,Fe,Mn)3(Si,Al)2O5(OH)4 |
ferromerrillite |
Ca9NaFe2+(PO4)7 |
ferropseudobrookite |
FeTi2O5 |
ferrosilite |
Fe2Si2O6 |
florenskyite |
(Fe,Ni)TiP |
fluorapatite |
Ca5(PO4)3F |
fluor-richterite |
Na2Ca(Mg,Fe)5Si8O22F2 |
forsterite |
Mg2SiO4 |
galena |
PbS |
galileiite |
NaFe4(PO4)3 |
gehlenite |
Ca2Al(SiAl)O7 |
geikielite |
MgTiO3 |
gentnerite (not approved) |
Cu8Fe3Cr11S18 |
gersdorffite |
NiAsS |
glauconite |
(K,Na)(Mg,Fe2+,Fe3+)(Fe3+,Al)(Si,Al)4O10(OH)2 |
goethite |
FeO(OH) |
gold |
Au |
gold-dominated alloys |
(Au,Ag,Fe,Ni,Pt) |
goldmanite |
Ca3V2(SiO4)3 |
graftonite |
(Fe,Mn)3(PO4)2 |
graphite |
C |
greenalite |
(Fe2+,Fe3+)2-3Si2O5(OH)4 |
greigite |
Fe3S4 |
grossite |
CaAl4O7 |
grossmanite |
CaTi3+AlSiO6 |
grossular |
Ca3Al2(SiO4)3 |
gupeiite |
Fe3Si |
gypsum |
CaSO4·2H2O |
haapalaite |
2[(Fe,Ni)S]·1.61[(Mg,Fe)(OH)2] |
halite |
NaCl |
hapkeite |
Fe2Si |
haüyne |
Na3Ca(Si3Al3)O12(SO4) |
haxonite |
(Fe,Ni)23C6 |
heazlewoodite |
Ni3S2 |
hedenbergite |
CaFeSi2O6 |
heideite |
(Fe,Cr)1.15(Ti,Fe)2S4 |
hematite |
Fe2O3 |
hemleyite |
FeSiO3 |
hercynite |
FeAl2O4 |
hexaferrum |
(Fe,Os,Ir,Mo) |
hexahydrite |
MgSO4·6H2O |
hexamolybdenum |
(Mo,Ru,Fe) |
hibbingite |
Fe2+2(OH)3Cl |
hibonite |
CaAl12O19 |
hibonite-(Fe) |
(Fe,Mg)Al12O19 |
hiroseite |
FeSiO3 |
hisingerite |
Fe2Si2O5(OH)4·2H2O |
hollisterite |
Al3Fe |
honessite |
(Ni,Fe)8SO4(OH)16·nH2O |
hornblende |
Ca2[Mg,Fe,Al]5[Si,Al]8O22(OH)2 |
hutcheonite |
Ca3Ti2(SiAl2)O12 |
hydromagnesite |
Mg5(CO3)4(OH)2·4H2O |
hydroxylapatite |
Ca5(PO4)3OH |
icosahedrite |
Al63Cu24Fe13 |
icosahedrite II |
Al62Cu31Fe7 |
idaite |
Cu5FeS6 |
illite |
K~0.65(Al,Mg,Fe)2(Si,Al)4O10(OH)2 |
ilmenite |
FeTiO3 |
indialite |
Mg2Al3(AlSi5O18) |
irarsite |
(Ir,Ru,Rh,Pt)AsS |
iridarsenite |
(Ir,Ru)As2 |
iron |
Fe |
isocubanite |
CuFe2S3 |
jadeite |
NaAlSi2O6 |
jarosite |
KFe3(SO4)2(OH)6 |
jimthompsonite |
(Mg,Fe)5Si6O16(OH)2 |
joegoldsteinite |
MnCr2S4 |
johnsomervilleite |
Na2Ca(Fe,Mg,Mn)7(PO4)6 |
kaersutite |
(Na,K)Ca2(Mg,Fe,Ti,Al)5(Si6Al2)O22O2 |
kaitianite |
Ti3+2Ti4+O5 |
kamiokite |
Fe2Mo3O8 |
kangite |
(Sc,Ti,Al,Zr,Mg,Ca,□)2O3 |
kanoite |
MnMgSi2O6 |
keilite |
(Fe,Mg)S |
keplerite |
Ca9(Ca0.5□0.5)Mg(PO4)7 |
khamrabaevite |
TiC |
khatyrkite |
CuAl2 |
kieserite |
MgSO4·H2O |
kirschsteinite |
CaFe(SiO4) |
K-Na-Fe phosphate |
(K,Na)Fe4(PO4)3 |
kosmochlor |
NaCrSi2O6 |
krinovite |
NaMg2CrSi3O10 |
krotite |
CaAl2O4 |
kryachkoite |
(Al,Cu)6(Fe,Cu) |
kuratite |
Ca2(Fe2+5Ti)O2[Si4Al2O18] |
kushiroite |
CaAlAlSiO6 |
kutnohorite |
CaMn(CO3)2 |
lakargiite |
CaZrO3 |
larnite |
Ca2SiO4 |
laurite |
RuS2 |
lawrencite |
(Fe2+,Ni)Cl2 |
lepidocrocite |
Fe3+O(OH) |
liebermannite |
KAlSi3O8 |
lime |
CaO |
lingunite |
NaAlSi3O8 |
linzhiite |
FeSi2 |
lipscombite |
(Fe2+,Mn)Fe3+2(PO4)2(OH)2 |
liuite |
FeTiO3 |
lizardite |
Mg3Si2O5(OH)4 |
löllingite |
FeAs2 |
loveringite |
Ca(Ti,Fe,Cr,Mg)21O38 |
machiite |
Al2Ti3O9 |
mackinawite |
(Fe,Ni)1+xS (x = 0-0.07) |
maghemite |
Fe2.67O4 |
magnéli phases |
Ti5O9 and Ti8O15 |
magnesio-arfvedsonite |
NaNa2(Mg4Fe3+)Si8O22(OH)2 |
magnesiochromite |
MgCr2O4 |
magnesioferrite |
MgFe2O4 |
magnesiohornblende |
Ca2(Mg4Al)(Si7AlO22)(OH)2 |
magnesiowüstite |
(Fe,Mg)O |
magnesite |
(Mg,Fe)CO3 |
magnetite |
Fe3O4 |
majindeite |
Mg2Mo3O8 |
majorite |
Mg3(MgSi)Si3O12 |
marcasite |
FeS2 |
margarite |
CaAl2(Si2Al2)O10(OH)2 |
marialite |
Na4(Si,Al)12O24Cl |
maricite |
NaFePO4 |
martensite (not approved) |
α2-(Fe,Ni) |
maskelynite |
(Na,Ca)(Si,Al)4O8 |
matyhite |
Ca9(Ca0.5☐0.5)Fe2+(PO4)7 |
maucherite |
Ni11As8 |
melanterite |
FeSO4·7H2O |
melilite |
(Ca,Na)2(Al,Mg)(Si,Al)2O7 |
melliniite |
(Ni,Fe)4P |
mendozite |
NaAl(SO4)2·11H2O |
mercury |
Hg |
merrihueite |
(K,Na)2(Fe,Mg)5Si12O30 |
merrillite |
Ca9NaMg(PO4)7 |
mica |
(K,Na,Ca)(Al,Mg,Fe)2-3(Si,Al,Fe)4O10(OH,F)2 |
millerite |
NiS |
moissanite |
SiC |
molybdenite |
MoS2 |
molybdenum (not approved) |
Mo |
molybdenum carbide (not approved) |
MoC |
monazite-(Ce) |
(Ce,La,Th)PO4 |
moncheite |
Pt(Te,Bi)2 |
monipite |
MoNiP |
monticellite |
CaMgSiO4 |
montmorillonite |
(Na,Ca)0.3(Al,Mg)2Si4O10(OH)2·nH2O |
moraskoite |
Na2Mg(PO4)F |
mullite |
Al6Si2O13 |
murchisite |
Cr5S6 |
muscovite |
KAl2(AlSi3O10)(OH)2 |
Na-Ca-Cr phosphate |
Na4CaCr(PO4)3 |
Na-Ca-Fe phosphate |
Na4Ca3Fe(PO4)4 |
Na-Fe-Mg phosphate |
Na2Fe(Mg,Ca)(PO4)2 |
Na-Mn-Fe phosphate |
Na4(Mn,Fe)(PO4)2 |
naquite |
FeSi |
Nb-oxide |
(Nb,V,Fe)O2 |
nepheline |
(Na,K)AlSiO4 |
nesquehonite |
Mg(CO3)·3H2O |
nickel |
Ni |
nickelblödite |
Na2(Ni,Mg)(SO4)2·4H2O |
nickeline |
NiAs |
nickelphosphide |
Ni3P |
nierite |
Si3N4 |
niningerite |
MgS |
niobium (not approved) |
Nb |
nontronite |
Na0.3Fe23+(Si,Al)4O10(OH)2.nH2O |
nuwaite |
Ni6GeS2 |
nyerereite |
Na2Ca(CO3)2 |
oldhamite |
CaS |
olivine |
(Mg,Fe)2SiO4 |
olkhonskite |
Cr2Ti3O9 |
omeiite |
(Os,Ru)As2 |
omphacite |
(Ca,Na)(Mg,Fe,Al)Si2O6 |
opal |
SiO2·nH2O |
orcelite |
Ni4.77As2 |
orthoclase |
KAlSi3O8 |
orthopyroxene |
(Mg,Fe)SiO3 |
osbornite |
TiN |
osmium |
Os |
osumilite |
KFe2(Al5Si10)O30 |
oxyphlogopite |
K(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2 |
panethite |
(Na,Ca,K)1-x(Mg,Fe,Mn)PO4 |
panguite |
(Ti,Al,Sc,Mg,Zr,Ca)1.8O3 |
paqueite |
Ca3TiSi2(Al,Ti,Si)3O14 |
paraotwayite |
Ni(OH)2-x(SO4,CO3)0.5x |
pecoraite |
Ni3Si2O5(OH)4 |
pentlandite |
(Fe,Ni)9S8 |
periclase |
MgO |
perovskite |
CaTiO3 |
perrierite-(Ce) |
(Ce,Nd,La,Ca,Th)4(Ti,Fe,Mg)5Si4O22 |
perryite |
(Ni,Fe)8(Si,P)3 |
PGE-dominated alloys |
(Pt,Os,Ir,Ru,Re,Rh,Mo,Nb,Ta,Ge,W,V,Pb,Cr,Fe,Ni,Co) |
phlogopite |
KMg3(Si3Al)O10(OH,F)2 |
pigeonite |
(Mg,Fe,Ca)2Si2O6 |
plagioclase |
(Na,Ca)(Si,Al)3O8 |
plagionite |
Pb5Sb8S17 |
platinum |
Pt |
poirierite |
Mg2SiO4 |
portlandite |
Ca(OH)2 |
potassic-chloro-hastingsite |
KCa2(Fe2+4Fe3+)(Si6Al2)O22Cl2 |
powellite |
CaMoO4 |
proxidecagonite |
Al34Ni9Fe2 |
pseudobrookite |
Fe2TiO5 |
pumpellyite-(Mg) |
Ca2(Mg,Fe2+)Al2(Si2O7)(SiO4)(OH)2·H2O |
pyrite |
FeS2 |
pyrochlore |
(Na,Ca)2Nb2O6(OH,F) |
pyrope |
Mg3Al2(SiO4)3 |
pyrophanite |
MnTiO3 |
pyroxferroite |
FeSiO3 |
pyrrhotite |
Fe1-xS |
quartz |
SiO2 |
rammelsbergite |
NiAs2 |
reevesite |
Ni6Fe3+2(CO3)(OH)16·4H2O |
reidite |
ZrSiO4 |
rhenium (not approved) |
Re |
rhodochrosite |
MnCO3 |
rhodonite |
CaMn4(Si3O15) |
rhönite |
Ca2(Mg,Al,Ti)6(Si,Al)6O20 |
ringwoodite |
Mg2SiO4 |
roaldite |
(Fe,Ni)4N |
roedderite |
(K,Na)2Mg5Si12O30 |
rubinite |
Ca3Ti3+2Si3O12 |
rudashevskyite |
(Fe,Zn)S |
rustenburgite |
(Pt,Pd)3Sn |
ruthenium |
(Ru,Os,Ir) |
ruthenium carbide (not approved) |
RuC |
rutheniridosmine |
(Ir,Os,Ru) |
rutile |
TiO2 |
safflorite |
CoAs2 |
sanidine |
KAlSi3O8 |
saponite |
(Ca,Na)0.3(Mg,Fe)3(Si,Al)4O10(OH)2·4H2O |
sapphirine |
(Mg,Al)8(Al,Si)6O20 |
sarcopside |
(Fe,Mn)3(PO4)2 |
scheelite |
CaWO4 |
schöllhornite |
Na0.3CrS2·H2O |
schreibersite |
(Fe,Ni)3P |
schwertmannite |
Fe3+16O16(OH,SO4)13-14·10H2O |
seifertite |
SiO2 |
selenium |
Se |
shenzhuangite |
NiFeS2 |
siderite |
FeCO3 |
silica with ZrO2-like structure (not approved) |
SiO2 |
sinoite |
Si2N2O |
slavikite |
NaMg2Fe3+5(SO4)7(OH)6·33H2O |
smythite |
(Fe,Ni)3+xS4 (x = 0-0.3) |
sodalite |
Na4(Si3Al3)O12Cl |
sodium-bearing silicate |
(Na,K,Ca,Fe)0.973(Al,Si)5.08O10 |
sodium-phlogopite |
(Na,K)Mg3(Si3Al)O10(F,OH)2 |
sperrylite |
PtAs2 |
sphalerite |
ZnS |
spinel |
MgAl2O4 |
spinelloid silicate |
(Mg,Fe,Si)2(Si,□)O4 |
spinelloid silicate-II |
(Fe,Mg,Cr,Ti,Ca,□)2(Si,Al)O4 |
stanfieldite |
Ca4(Mg,Fe)5(PO4)6 |
starkeyite |
MgSO4.4H2O |
steinhardtite |
(Al,Ni,Fe) |
stilbite-Ca |
NaCa4(Si27Al9)O72·30H2O |
stishovite |
SiO2 |
stöfflerite |
CaAl2Si2O8 |
stolperite |
AlCu |
suessite |
Fe3Si |
sulfur |
S |
sylvite |
KCl |
szomolnokite |
FeSO4·H2O |
taenite |
(Fe,Ni) |
talc |
Mg3Si4O10(OH)2 |
tazheranite |
(Zr,Ti,Ca,Y)O1.75 |
tetragonal almandine |
(Fe,Mg,Ca,Na)3(Al,Si,Mg)2Si3O12 |
tetragonal majorite |
Mg3(MgSi)Si3O12 |
tetrataenite |
FeNi |
thénardite |
Na2SO4 |
thorianite |
ThO2 |
thortveitite |
Sc2Si2O7 |
Ti3+,Al,Zr-oxide |
(Ti3+,Al,Zr,Si,Mg)1.95O3 |
Ti-oxide |
Ti3O5 |
Ti-rich magnetite |
(Fe,Mg)(Fe,Al,Ti)2O4 |
tilleyite |
Ca5Si2O7(CO3)2 |
tissintite |
(Ca,Na,□)AlSi2O6 |
tistarite |
Ti2O3 |
titanite |
CaTiSiO5 |
tochilinite |
6(Fe0.9S)·5[(Mg,Fe,Ni)(OH)2] |
tranquillityite |
Fe2+8Ti3Zr2Si3O24 |
transjordanite |
Ni2P |
trevorite |
NiFe2O4 |
tridymite |
SiO2 |
troilite |
FeS |
tsangpoite |
Ca5(PO4)2(SiO4) |
tschaunerite |
Fe2+(Fe2+Ti4+)O4 |
tugarinovite |
MoO2 |
tuite |
Ca3(PO4)2 |
tungstenite |
WS2 |
uakitite |
VN |
ulvöspinel |
Fe2TiO4 |
V,Fe,Cr-rich sulfide |
(V,Fe,Cr)4S5 |
V-rich brezinaite |
(Cr,V,Fe)3S4 |
V-rich daubréelite |
Fe(Cr,V)2S4 |
V-rich magnetite |
(Fe,Mg)(Fe,Al,V)2O4 |
valleriite |
2[(Fe,Cu)S]·1.53[(Mg,Al)(OH)2] |
vaterite |
CaCO3 |
vermiculite |
(Mg,Fe,Al)3(Si,Al)4O10(OH)2·4H2O |
vestaite |
(Ti4+Fe2+)Ti4+3O9 |
violarite |
FeNi2S4 |
vivianite |
Fe3(PO4)2·8H2O |
voltaite |
K2Fe2+5Fe3+3Al(SO4)12·18H2O |
wadalite |
Ca6Al5Si2O16Cl3 |
wadsleyite |
Mg2SiO4 |
wairauite |
CoFe |
wangdaodeite |
FeTiO3 |
warkite |
Ca2Sc6Al6O20 |
wassonite |
TiS |
whewellite |
CaC2O4·H2O |
wilkinsonite |
Na2Fe2+4Fe3+2Si6O20 |
winchite |
☐NaCa(Mg4Al)Si8O22(OH)2 |
wollastonite |
CaSiO3 |
wurtzite |
ZnS |
wüstite |
FeO |
xenophyllite |
Na4Fe7(PO4)6 |
xenotime-(Y) |
YPO4 |
xieite |
FeCr2O4 |
xifengite |
Fe5Si3 |
yagiite |
(Na,K)1.5Mg2(Al,Mg)3(Si,Al)12O30 |
zagamiite |
CaAl2Si3.5O11 |
zaratite |
Ni3(CO3)(OH)4·4H2O |
zeolite group |
(Na,K)0-2(Ca,Mg)1-2(Al,Si)5-10O10-20.nH2O |
zhanghengite |
(Cu,Zn) |
zircon |
ZrSiO4 |
zirconium carbide (not approved) |
ZrC |
zirconolite |
CaZrTi2O7 |
zirkelite |
(Ti,Ca,Zr)O2-x |
Notes
1. Exsolution lamellae are thin laths of one mineral phase within another. They form in the solid state during cooling for specific compositions when the crystal structure of the parent mineral phase encounters a miscibility gap and can no longer accommodate the entire set of cations it was able to retain at higher temperature. For example, at high temperature, troilite can accommodate significant amounts of Cr, but during cooling, thin lamellae of daubréelite (FeCr2S4) can exsolve.
