Vein graphite, also known as crystalline vein graphite, Sri Lankan graphite, or Ceylon graphite is a naturally occurring form of pyrolytic carbon (solid carbon deposited from a fluid phase). Vein graphite has a morphology that ranges from flake-like for fine particles, needle or acicular for medium sized particles, and grains or lumps for very coarse particles. As the name implies, this form of graphite occurs as a vein mineral. Vein fillings range in thickness from 1 to 150 cm. “As mined” material is available in sizes ranging from fine powder to 10 cm lumps.
Vein graphite has the highest “degree of crystalline” perfection of all conventional graphite materials. As a result of its high degree of crystallinity, vein graphite is utilized extensively in “formed” graphite products that are used in electrical applications. Many of the highest quality electrical motor brushes and other current carrying carbons are based on formulations using vein graphite. In friction applications, vein graphite is used in advanced brake and clutch formulations. Other applications include most of those that can utilize flake graphite. Commercial grades are available in purities ranging from 80-99% carbon, and sizes from 3-micrometer powder to 8-10 cm lumps.
Amorphous graphite is a naturally occurring seam mineral that forms from the geologic metamorphism of anthracite coal. Contrary to the name, “amorphous” graphite is not truly amorphous, but is a microcrystalline form of natural graphite. The morphology of amorphous graphite is typically granular except in extremely fine grinds, which have a flaky structure. The term “amorphous” is applied to this form of natural graphite because the extremely small “crystallite” particles that make this material do not form crystal faces that are visible to the naked eye (anhedral opposed to euhedral.) “As mined” material is available in sizes ranging from mixed 1 cm and smaller particles to 10 cm lumps.
Flake graphite is a naturally occurring form of graphite that is typically found as discrete flakes ranging in size from 50 to 800 micrometers in diameter and 1-50 micrometers thick. This form of graphite has a high degree of “crystallinity”, which equates to near theoretical true density, high thermal and electric conductivity, and low springback (excellent molding characteristics.) Flake graphite is used in many applications including but not limited to powder metallurgy, fuel cell bi-polar plates, coatings, thermal materials, friction moderators, electrically conductive materials, refractories, general lubricant applications, pencils, gaskets, rubber compounds, other advanced polymer systems. Commercial grades are available in purities ranging from 80-99.9% carbon, and sizes from 2 to 800 micrometers.
Flake graphiteis found in metamorphic rocks uniformly distributed through the body of the ore or in concentrated lens shaped pockets. Carbon concentrations vary between 5% and 40%. Graphite flake occurs as a scaly or lamella form in certain metamorphic rocks such as limestone, gneisses and schists.