an unusual large specimen of natural graphite
Graphite, like diamond, is a form of pure carbon, a naturally occurring form of crystalline carbon. The carbon atoms are joined together in hexagonal arrays in two-dimensional sheets stacked one on top of another. This gives it its characteristic basal cleavage and flaking, which imparts a greasy feel and gives it lubricant properties. Graphite is also known as plumbago or black lead. Its softness and black streak have long made it a writing tool, especially in pencils. It is also used in crucibles, electrodes, generator brushes, and as a moderator to slow down neutrons in atomic reactors. Its colour, streak and lower specific gravity distinguish it from molybdenite. Graphite is formed mainly when sediments rich in organic matter are metamorphosed.
It is a native element mineral found in metamorphic and igneous rocks. Graphite is a mineral of extremes. It is extremely soft, cleaves with very light pressure, and has a very low specific gravity. In contrast, it is extremely resistant to heat and nearly inert in contact with almost any other material. These extreme properties give it a wide range of uses in metallurgy and manufacturing.
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