When the figure is not level people cannot know what is meant by width, depth, or height without being told (or without labels), although length is generally still assumed to mean the direction in which the figure is longest..
The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.oal is primarily used as a solid fuel to produce electricity and heat through combustion. World coal consumption was about 7.25 billion tonnes in 2010 (7.99 billion short tons) and is expected to increase 48% to 9.05 billion tonnes (9.98 billion short tons) by 2030.
Coal is a combustible sedimentary rock composed mostly of carbon and hydrocarbons. It is the most abundant fossil fuel produced in the United States, but it is a nonrenewable resource.The energy in coal comes from the energy stored by plants that lived hundreds of millions of years ago in swampy forests.t is the most commonly used type of coal for electric power generation in the United States. It is a dark, hard coal that has a higher heating value than lignite and subbituminous coal, but a lower heating value than anthracite.