Graphite mineral, we also called graphite occurrences.
Natural graphite occurs in a variety of geological settings around the globe. Economically viable deposits are generally associated with the graphitization of organic, carbon-rich precursors through process, specifically medium-pressure and medium-to-high temperature metamorphism of organic, carbon-rich precursor materials. The grade of metamorphism deter mines crystallinity, thus allowing classification into three physically distinct deposit types referred to as microcrystlline(also called amorphous), vein(lump or chip), and crystalline(flake) graphite by the graphite industry, the latter two being the most commercially viable.
Amorphous graphite deposits, also called cryptocrystalline or microcrystalline graphite, are associated with lower-grade metamorphism(sub-greenschist to greenschit facies), contact metamorphism or regional metamorphism of coal seams. Amorphous graphite deposits vary in grade between 30% and 95% carbon, and typically consist of predominantly very fine to fine-grained graphite flake. The term amorphous is somewhat misleading, as amorphous graphite, despite its name, still exhibits a crystalline structure.
Higher-grade(upper amphibolite to granulite facies) metamorphism creates progressively more crystalline flake and vein graphite deposits.
Macrocrystalline graphite deposits, referred to commercially as flake graphite, present as disseminated graphite flakes in a variety of rocks such as paragneiss and marble. Graphite crystals present in the form of discrete macrocrystalline, disseminated flakes and are commercially classfied into flake size categories such as jumbo, large, medium, small and fine flakes, with large and jumbo flake sizes commanding the highest prices. Flake graphite deposits with a favourable flake size distribution towards large and jumbo flakes are the most sought after. Grade range between 3% and 30% C and typically increase with flake size.
Vein graphite deposits, commonly referred to as lump or chip graphite in the industry, are a type of crystalline graphite deposit and occur as epigenetic veins and lodes from metamorphic fluids in the same metasedimentary belts as flake deposits. Veins vary in thickness from a few millimeters to over 1 meter, with most vein deposits less than 30 cm thickness. Flakes can exceed 4mm in size and often exhibit exceptional purity and near-perfect crystals. Grades are typically highes in vein graphite deposits, reaching up to 90% and more. Sri Lanka is currently the sole commercial source of vein graphite.
In addition to resource tonnage and grade, flake size distribution and purity are considered key attributes when assessing the quality of graphite projects and the salability of the product. Purity, in particular, plays a major role in determining whether the end product from a specific deposit is suitable for consumption in high-value applications such as lithium-ion batteries. Typically, the purity of the end product increase with the size of the flakes in a deposit. More often than not, the marketing strategies of the respective company depend on the end user they are trying to attract.