Opaque form of Element commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. Click on Term to Read More (C) found in some iron and ordinary Chondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have identical physical properties, except for their Mutual arrangement of atoms, molecules or ions that are packed together in a crystal lattice to form a crystal. Click on Term to Read More. Naturally occurring graphite contains up to 30% of the β form; synthetically produced graphite only contains the α form. The α form can be converted to the β form through mechanical treatment; the β form reverts to the α form when heated above 1000 °C.
Egg-shaped graphite nodules are found in a number of meteorites. These nodules are often referred to as “primary structures” in iron meteorites. Most nodules have rims of Less common than kamacite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Taenite, γ-(Fe,Ni), has 27-65 wt% Ni, and forms small crystals that appear as highly reflecting thin ribbons on the etched surface of a meteorite; the name derives from the Greek word for "ribbon." Click on Term to Read More and Ni-Fe phosphide mineral, (Fe,Ni)3P, yellowish in color and predominantly found in iron and stony-iron meteorites. Schreibersite can also be found in a variety of other meteorites including some acapulcoites, aubrites, enstatite chondrites and achondrites, lunars, ureilites, winonaites and a smattering of other meteorite types like CM, CO and CB. Schreibersite Click on Term to Read More that has precipitated on the nodules during cooling and Physical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. Click on Term to Read More. The enveloping taenite is highly resistant to weathering.
Some or all content above used with permission from J. H. Wittke.