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.
Coal mining year. The United States was ranked as the second highest coal producing country in the world in 2010, and possesses the largest coal reserves in the world. In 2008 then-President George W. Bush stated that coal was the most reliable source of electricity. However, in 2011 President Barack Obama said that the US should rely more on "clean" sources of energy that emit lower or no carbon dioxide pollution. For a time, while domestic coal consumption for electric power was being displaced by natural gas, exports were increasing. US net coal exports increased ninefold from 2006 to 2012, peaked at