Flake Graphite and Vein Graphite
both form by precipitation of carbon in a high-temperature, high-pressure environment.
Sources of the free carbon atoms might be magmatic, thermal decomposition of carbonates,
or pyrolysis of organic matter. The free carbon is transported from the source to the
location where it precipitates as a crystal. Flake and vein graphite tend to be the purest
forms (high grade) and have the best electrical and thermal properties, and therefore
command the highest prices. Both types are found at the Ruby Graphite property.
Flake Graphite is found as disseminated
crystals in a host rock which is commonly granite, pegmatite, gneiss, schist and on
occasion, marble or other metamorphic rock types.
Vein Graphite forms by the same mechanism as
flake graphite, but the precipitation occurs within open fissures, fractures, vugs or
other spaces within the host rock, resulting in massive crystal bodies ranging from thin
individual veinlets to thick pods to stockwork-type vein groups. Disseminate flake
graphite is often found in the host rock surrounding vein graphite.
Amorphous Graphite is a micro-crystalline
form and is the result of in-place metamorphism of organic material such as a coal seam
or carbonaceous shale. North American examples of amorphous graphite are the small
occurrences in New England and the large deposit in Sonora, Mexico. Amorphous graphite
is the least pure form, having the highest mineral content, has the poorest electrical
properties, has the greatest availability with large production from China, and is
therefore the least valuable form of graphite.
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Sample RG Bird's Nest: Massive platy and
tabular vein graphite (red arrow) with minor non-sulfide gangue host rock (green arrow)
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Sample RG G-0: Disseminated flake graphite (red
arrows) with massive non-sulfide gangue host rock (green arrows)
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