Graphite extraction is based on the degree of weathering of the ore rock and the proximity of the ore to the surface. Around the world, graphite is mined using two techniques: the open pit method (surface quarrying) and the underground method. Natural graphite is classified into flake or microcrystalline graphite, macrocrystalline graphite, and vein or lump graphite based on its underlying physical and chemical properties. These three types of graphite have distinct characteristics as a result of their occurrence in different geological regions. Flake graphite and macrocrystalline graphite are mined open pit and underground, whereas lump graphite, sourced by Sri Lanka, is only mined underground.
Open pit mining involves extracting rock or minerals from an open pit or burrow. Open pit methods are used when the ore is close to the earth and the surface material covering the deposit is thin. Quarrying is a form of surface mining employed to obtain graphite by breaking the rocks either by drilling or by using dynamite explosives to cut open the rocks and compressed air or water to split it. Bore hole mining that is common to both open pit and underground methods involves drilling a hole to reach the ore, making a slurry using water through a tube and pumping back the water and mineral to the storage tank for further processing. Drilling and blasting methods are used on hard rock ore to liberate large-sized graphite flakes that are then crushed and ground before being subjected to flotation. The extracted graphite is brought to the surface by locomotives or, in developing countries, handpicked, shoveled and pulled in a cart and moved to the plant for further processing.
Underground mining is done when the ore is present at a greater depth. Drift mining, hard rock mining, shaft mining and slope mining are exclusive to underground mining and are employed in graphite extraction. Underground mining is basically performed in two ways: Room and pillar mining, a mechanized extraction method wherein the pillars formed by the coal hold up the roof that caves in with mine closing as a result of the pillars being mined, and the much safer longwall or continuous mining by which only layers of the mineral are extracted from the pillars.
Shaft mining is employed to reach the deepest ores. There are shafts or tunnels for men and heavy equipment to move in and out. A different shaft is used for transportation of extracted ore and an air shaft for ventilation. Slope mining is done with slanted shafts that are not too deep and helps to extract ore that occurs parallel to the ground. Conveyors are used for transporting men and load using separate shafts. Drift mining, mostly done in mountainous regions, is common in the eastern U.S.; it has horizontal tunnels made lower than the mineral vein for gravity-aided extraction.