meteorite minerals

Metallic Iron   
Iron Sulfides  
Iron Carbides
Phosphides  
Oxides   
Carbon   
Silicate Minerals
How to Identify Meteorites (separate file)
Meteorites (separate file)
Meteorite Cratering on Earth(separate file)


 The following descriptions of meteorite minerals are not exhaustive, but should give you an idea of some of the important components of meteorites.

Metallic Iron

Metallic iron minerals make up the largest percentage of iron meteorites and stony iron meteorites. They are also important in chondrites.

Kamacite- -this is essentially metallic iron with up to 7.5% nickel in solid solution. In cut sections kamacite looks like metallic iron and like the other important nickel-iron mineral, taenite. On etched and polished surfaces, sometimes it can be distinguished. Kamacite may have Neumann bands--lines that are created when meteorites are shocked. Kamacite occurs as rims around troilite or schreibersite--swathing kamacite. Sometimes on polished surfaces, kamacite may be distinguished from taenite because it is not as hard.

Taenite --this is iron with more than 25 percent nickel in solid solution. The atoms of taenite arrange themselves in a cube form with an atom centered in the face. In non-meteoritic metals this mineral is called austenite. Taenite is resistant to the nitol etching process, thus the plates of taenite stand out after the etching process. Polishing sometimes allows one to distinguish taenite. Because it is harder it stands out.

Plessite- -this is not a mineral, but is a mixture of fine-grained kamacite and taenite. Scientists have distinguished several types of plessite based on microscopic structures.

Iron Sulfides

Troilite --FeS--Iron sulfide similar to the earthly mineral pyrrhotite. Troilite is not magnetic. It is metallic with a slight bronze color and slight greenish tint. It occurs as spherical or rounded nodules. Sometimes troilite occurs as plates (lamellae) parallel to the cubic structure of the cubic taenite structure of iron meteorites. With a few exceptions, troilite is present in most iron meteorites.

Daubreelite --FeCr2S4--This iron chrome sulfide is found as exsolution lamellae in troilite nodules or as particles in kamacite.

Iron Carbides

Cohenite --(Fe,Ni,Co)3C--is iron carbonate it is closely related to cementite (Fe3C), a mineral described in steel. It is brilliant silver. The crystal form is orthorhombic. Cohenite is extremely hard and will quickly dull saw blades. Cohenite is unstable at atmospheric temperatures and pressures and over a long period of time will break down into kamacite and graphite.

Haxonite- -(Fe,Ni,Co)23C6--is a cubic iron carbide similar to minerals found in steel. It to is hard, though not as hard as Cohenite. It is bright silver. Like Cohenite, it is unstable at atmospheric temperatures and pressures and will gradually decompose to kamacite and graphite.

Phosphides

Schreibersite and Rhabdite --(Fe,Ni)3P--Iron-nickel phosphide. Schreibersite is yellowish metallic, very hard--though not as hard as Cohenite--brittle, and magnetic. The crystal form appears as oriented plates in the matrix of kamacite and taenite. Plate shaped Rhabdites are found in hexahedrites.

Oxides

Chromite --FeCrO4--This ore of chrome is common on earth and as a trace mineral in iron meteorites. It is black, with cubic crystal form and octahedral cleavage.

Magnetite- -Fe3O4--A common ore of iron on earth is found in the crusts of most meteorites and in carbonaceous chondrites. Magnetite is submetallic black with cubic crystal form and octahedral cleavage.

corundum --Al2O3--This mineral is what rubies and sapphires are made of--it is also a trace mineral in meteorites. Dont look for red or blue. Gray is the probable color.
 
 

Carbon

Graphite- -C--The common mineral of pencil lead is common as nodules in Iron meteorites and in carbonaceous chondrites. It is black and very soft.

Diamond --C--This is the same element as graphite. When graphite is subjected to the extraordinarily high temperature and pressure of meteorite impact, sometimes diamonds will form. Canyon Diablo meteorites have some.

Lonsdaleite --C--A hexagonal polymorph of diamond (diamond is cubic). Lonsdaleite is mixed with diamond at Canyon Diablo.
 
 

Silicate Minerals

Pyroxenes --A group of mostly dark colored rock-forming minerals common on Earth and in meteorites. Orthopyroxenes are a subcatagory that are found in meteorites--particularly chondrites and achondrites. The following is a list of a solid solution series that gradually decreases in magnesium and increases iron content:
 
 
  • Enstatite --Mg2Si2O6--The end member--the one highest in magnesium. It is grayish to yellowish to brown and an important rock former on Earth. In meteorites it is a key constituent of the rare enstatite chondrite.
  • Bronzite- -(Mg,Fe)SiO3--This member is usually brown or green and often having a pearly luster. It has more iron than enstatite and more magnesium than hypersthene.
  • Hypersthene --(Mg,Fe)SiO3--This mineral is similar to bronzite in many ways, but having more iron, it will tend to be darker--even black.
  • Orthoferrosilite --FeSiO3--This is the other orthopyroxene end member. It has the most iron and the least magnesium.
  • Clinopyroxenes , (monoclinic crystal structure) diopside (CaMg(SiO3)2), hedenbergite (CaFeSi2O6), augite ((Ca,Na)(Mg,Fe,Al)(Si,Al)2O6) and pigeonite ((Mg,Fe,Al)(Mg,Fe)Si2O6) are also found in meteorites particularly achondrites.

  • Olivine --(Mg,Fe)2SiO4--is a rock forming mineral on Earth that is believed to have been formed at great depth. The Earth's mantle may have significant olivine. In meteorites, olivine is important in some pallasites. The olivines are a solid solution series with forsterite containing the most magnesium and fayalite having the most iron. The olivine in most stony iron meteorites ranges in composition from 60 to 85 percent forsterite with the remainder being fayalite.

    Feldspars- -calcium, sodium. aluminum silicates-- (courtesy of S. Ray DeRusse with thanks of www.bccmeteorites.com) are found in meteorites especially with respect to Achondrites which are generally differentiated by temperature and or pressure.
    These samples contain abundant Feldspar as much as 35 percent for highly differentiated samples.
    The remainder is cristobalite, tridymite,  pyroxene and reduced metals such as iron and titanium oxides with minor accessories.
    It would be much better to say 3 end member Feldspars because if  your sample contains anorthite this implies a hi Tc meaning it has to cool at some point resulting in albite as the other end member.Na is isomorphous with Ca and K  but K is not isomorphous with Ca]. In the solid solution series Ca will be used up first (high Tc) and any left over Na will go into solution with K.
     
    Therefore the entire range of Feldspars will generally be present. (Not just two or three).
    However Feldspars are rare in Iron-Nickel meteorites but very common minerals in stony meteorites.  There are two main groups of feldspars, plagioclase and orhtoclase. Each group is broken down into several intermediate members depending on the calcium and sodium content. Plagioclase is more common and noted varieties include albite, oligoclase, labradorite, bytownite, and anorthite.

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