Meteoric Minerals

Meteoric Minerals include the minerals common to known asteroids and meteorites, plus many minerals only (or at least primarily) found in meteorites. Note that many - likely most - minerals on Earth are the result of many cycles of formation, breakdown, and reformation under changing conditions including the presence of liquid water and free oxygen, and thus could not exist in primitive materials. As few as 60 distinct minerals may have initially formed in the early solar system, with the remaining thousands of known minerals all formed by subsequent reprocessing - many of which may only be possible as a result of the changes created by life on Earth, including the presence of free oxygen. (See The Evolution of Minerals.)

Chondrites (primitive asteroids including most stony meteorites) come in several varieties. Carbonaceous chondrites largely mimic the elemental composition of the solar nebula, minus the lighter volatiles. Their spectra often reveal evidence of the (past) presence of liquid water in the form of iron-rich clays, serpentine group minerals such as cronstedtite (Fe2+2Fe3+(Si,Fe3+O5)(OH)4), and the carbonate minerals dolomite (CaMg(CO3)2) and siderite (FeCO3).

The ordinary chondrites largely mimic the composition of the Earth's mantle, and generally include a mixture of chondrules that each formed under either reducing and oxidizing conditions. Minerals include fosterite (Mg2SiO4), enstatite (MgSiO3), metallic iron (Fe), and troilite (FeS) when formed under reducing conditions, and olivine ((Mg,Fe)2SiO4), hypersthene ((Mg,Fe)SiO3), and magnetite (Fe3O4) when formed under oxidizing conditions.

Enstatite group carbonaceous chondrites contain some of the most reduced minerals known, including osbornite (TiN), sinoinite (SiNO), cohenite (Fe3C), schreibersite ((Fe, Ni)3P), troilite (FeS), oldhamite (CaS), niningerite (MgS), and perryite (Fe-Ni silicide).

The light-colored Calcium-Aluminum-rich Inclusions (or CAI's) common in carbonaceous chondrites are composed of refractory minerals including anorthite (CaAl2Si2O8), hibonite ((Ca,Ce)(Al,Ti,Mg)12O19), melilite (Ca2Al2SiO7), perovskite (CaTiO3), pyroxenes such as hedenbergite (CaFeSi2O6) and diopside (CaMgSi2O6), spinel (MgAl2O4), and additional forsterite-rich olivine (very little iron is present).

Iron and stony-iron meteorites differ largely by the presence of stony material such as olivine ((Mg,Fe)2SiO4), including the gem variety peridot in pallasite meteorites. The iron is always alloyed with nickel in proportions ranging from 5% to as much as 25%. As they slowly cooled, the different alloys might separate (thus visible in Widmanstatten patterns) into the minerals kamacite (Fe0.9Ni0.1) and taenite (Fe0.8Ni0.2). Even iron meteors commonly contain inclusions such as troilite (FeS), graphite (C), schreibersite ((Fe,Ni)3P), and cohenite ((Fe,Ni,Co)3C).

There are many minerals commonly found in meteorites (and thus asteroids) which are extremely rare on Earth, including moissanite (SiC), schreibersite (Fe,Ni)3P, and xifengite (Fe5Si3).

Tiny diamonds (C) have also been found in meteorites, but the most common gemstone found in meteors by far is peridot (the gem variety of olivine); some stony-iron meteors may be sliced and polished resulting in a beautiful stained-glass-window appearance of green peridot crystals in an iron matrix.

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