Opaque form of carbon (C) found in some iron and ordinary chondrites 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 crystal structure. 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 taenite and schreibersite that has precipitated on the nodules during cooling and crystallization. The enveloping taenite is highly resistant to weathering.

Some or all content above used with permission from J. H. Wittke.

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