Colors in shale are caused by the presence of certain minerals and organic substances. Black shale, for example, results from organic matter, red shale from ferric iron, and green shale from ferrous iron. Shale is soft and porous, characteristics that allow it to absorb and release organic matter and minerals easily. Trapped organic material may be converted into petroleum and other hydrocarbons. Shale has considerable economic value.
Oil is extracted from shale in the United States, Brazil, and South Africa.
Petroleum from this source, however, cannot be refined by methods used for crude oil. To render shale oil usable, hydrogen must be added and the mixture treated chemically to remove nitrogen and impurities. Shale in the eastern United States is a rich source of uranium. A large band of this sedimentary rock in Central Europe contains metallic sulfides, and shale deposits in eastern Germany and Poland are mined for their copper, lead, and zinc. The Learning Company, Inc.