There are three types of natural graphite: amorphous, flake, and vein or lump. Amorphous graphite is the most abundant type and also the lowest quality.  Amorphous is used for lower value graphite products and is the lowest priced graphite. Flake graphite is higher quality than amorphous and it occurs as plates that are crystallized in metamorphic rock. This type of graphite can be used for such things as flame retardant substances. Vein or lump graphite is the rarest and most valuable form of graphite.

http://en.wikipedia.org/wiki/Carbon,

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