Flake graphite
Vein graphite

Graphite Resources

There are three forms of naturally occurring graphite: amorphous graphite, flake graphite and hydrothermal vein graphite with large flake and vein graphite deposits being most valuable.

Most important factors that determine the value of a graphite deposit include: carbon content, flake size, type and levels of impurities, deposit size and amenability.

Flake graphite is a naturally occurring form of graphite with graphite crystals present in the form of discrete flakes. Individual flakes can be easily recognized by naked eye with typical sizes ranging from fine (<150 µm or 100 mesh) to coarse (>150 µm). Typically graphite occurs as disseminated flakes in metamorphic rocks (e.g gneisses) displaying carbon grades ranging from 5 to 30 wt.-%. Such can be concentrated by physical processing and purified by advanced thermal technology and chemical purification techniques into high purity products +99.9 wt.-%. Specifically large flake sizes are sought after since they are needed for high purity, technology grade graphite applications such as the production of spherical graphite used in Li-ion batteries. Graphite flakes are made up of parallel sheets of carbon atoms in a hexagonal arrangement. It is possible to insert other chemical species between the sheets, a process termed intercalation, thereby modifying its structure and tuning its physical and chemical properties. Graphite can be intercalated with sulfuric and nitric acids which will serve as a feed material for production of expanded graphite from which foils are formed that are used in seals, gaskets, and fuel cells.
Large flake grades make just over 20% of total flake graphite output of 375,000 tonnes in 2013, and with competition for these grades from other traditional markets (i.e. the refractories sector), new projects are likely to be required to meet the battery market demand.
Flake graphite deposits are generally found at or near surface and are therefore amenable to open-pit mining. There are significant flake graphite deposits in China, India, Brazil, Germany, Canada and North Korea with recent production dominated by China (60%) and Brazil (23%).

Hydrothermal vein graphite is the rarest and most pure type of naturally occurring graphite. As opposed to flake and amorphous graphite it has formed by deposition from high temperature (hydrothermal) carbonaceous fluids, filling steeply inclined veins and fissures in the surrounding host rock. Vein graphite is present in the form of coarse (exceeding 4 mm), platy or needle-like crystals which are recovered in the form of lumps from cm to meter scaled graphite veins. Typically vein graphite deposits show natural purities in excess of 90 wt.-% graphitic carbon. Veins are mined using conventional shaft or surface methods. Typical carbon contents in hydrothermal vein graphite products are in the range 98 to 99.9 wt.-% graphitic carbon. Due to its exceptional purity and highly perfect crystals vein graphite products show superior thermal, electrical and mechanical properties compared to amorphous and flake graphite in certain applications. Vein graphite deposits can be found in Sri Lanka, Great Britain, Canada and in other places; sole commercial source of vein graphite to date is Sri Lanka.

Amorphous graphite is a term used for microcrystalline graphite occurring in masses that consist of individual very fine graphite crystals at the µm-scale that can’t be resolved by naked eye or optical microscopy. It is the most abundant form of graphite. It is typically formed from anthracite, i.e. thermally metamorphosed coal seams during a metamorphic event, i.e. the action of temperature or pressure due to intrusion of a magmatic body or a tectonic event. Amorphous graphite deposits typically show total graphitic carbon contents (TGC) ranging from 20 to 40 wt.-%, while amorphous graphite products will be in the range 70 to 85 wt.-%. Therefore, amorphous graphite is typically lower in purity than other natural graphite. This is due to an intimate contact between graphite micro crystals and the mineral impurity phases with which it is associated. This close graphite/impurities association makes flotation and other density and chemical based separation techniques inefficient if not impossible.
Due to its limited purity and flake size amorphous graphite is mainly used in standard commodities (lubricants, brake linings, refractories, steelmaking where higher ash contents are acceptable) and is the lowest priced graphite. Major deposits of amorphous graphite are found in China, Mexico; there are also deposits in the US and in Europe.