Carbon the very large masses of carbonate rock (limestone, dolomite, marble and so on). Coal is very rich in carbon (anthracite contains 92–98%) and is the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil fuel. As for individual carbon allotropes, graphite is found in large quantities in the United States (mostly in New York and Texas), Russia, Mexico, Greenland, and India. Natural diamonds occur in the rock kimberlite, found in ancient volcanic "necks", or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Sierra Leone.
Pittsburgh coal seam matter (gases expelled when coal is burned), leaving carbon and ash from the coal fused together in the form of coke. They made coke in turf-covered "mounds," in which coal burned slowly and without oxygen to drive off impurities. The adoption of beehive coke ovens in the 1830s spurred the use of Pittsburgh-seam coal in iron furnaces, and these ovens made better-quality coke than mounds. Pittsburgh-seam coal, especially the highest-quality coal found in the Connellsville district, was the best coal in America for making coke. When converted into coke, it was sufficiently strong to withstand the weight of iron ore