area strip mining Type of surface mining used where the terrain is flat. An earthmover strips away the overburden, and a power shovel digs a cut to remove the mineral deposit. After removal of the mineral, the trench is filled with overburden, and a new cut is made parallel to the previous one. The process is repeated over the entire site. Compare dredging, mountaintop removal, open-pit mining, subsurface mining. 

bitumen Gooey, black, high-sulfur, heavy oil extracted from tar sand and then upgraded to synthetic fuel oil. See tar sand. 

breeder nuclear fission reactor Nuclear fission reactor that produces more nuclear fuel than it consumes by converting nonfissionable uranium-238 into fissionable plutonium-239.

chemosynthesis Process in which certain organisms (mostly specialized bacteria) extract inorganic compounds from their environment and convert them into organic nutrient compounds without the presence of sunlight. Compare photosynthesis. 

coal Solid, combustible mixture of organic compounds with 30-98% carbon by weight, mixed with various amounts of water and small amounts of sulfur and nitrogen compounds. It forms in several stages as the remains of plants are subjected to heat and pressure over millions of years.

coal gasification Conversion of solid coal to synthetic natural gas (SNG). 

coal liquefaction Conversion of solid coal to a liquid hydrocarbon fuel such as synthetic gasoline or methanol. 

contour strip mining Form of surface mining used on hilly or mountainous terrain. A power shovel cuts a series of terraces into the side of a hill. An earthmover removes the overburden, and a power shovel extracts the coal, with the overburden from each new terrace dumped onto the one below. Compare area strip mining, dredging, mountaintop removal, open-pit mining, subsurface mining. 

core Inner zone of the earth. It consists of a solid inner core and a liquid outer core. Compare crust, mantle.

crude oil Gooey liquid consisting mostly of hydrocarbon compounds and small amounts of compounds containing oxygen, sulfur, and nitrogen. Extracted from underground accumulations, it is sent to oil refineries, where it is converted to heating oil, diesel fuel, gasoline, tar, and other materials. 

depletion time Time it takes to use a certain fraction, usually 80%, of the known or estimated supply of a nonrenewable resource at an assumed rate of use. Finding and extracting the remaining 20% usually costs more than it is worth. 

deuterium (D; hydrogen-2) Isotope of the element hydrogen, with a nucleus containing one proton and one neutron and a mass number of 2. 

dredging Type of surface mining in which chain buckets and draglines scrape up sand, gravel, and other surface deposits covered with water. It is also used to remove sediment from streams and harbors to maintain shipping channels. See dredge spoils. Compare area strip mining, contour strip mining, mountaintop removal, open-pit mining, subsurface. 

Economic depletion Exhaustion of 80% of the estimated supply of a nonrenewable resource.Finding, extracting, and processing the remaining 20% usually costs more than it is worth; may also apply to the depletion of a renewable resource, such as a fish or tree species.

Exhaustible resource See nonrenewable resource. 

Fissionable isotope Isotope that can split apart when hit by a neutron at the right speed and thus undergo nuclear fission. Examples are uranium-235 and plutonium-239. See nuclear fission.

gangue Waste or undesired material in an ore. See ore. 

high-quality energy Energy that is concentrated and has great ability to perform useful work.Examples are high-temperature heat and the energy in electricity, coal, oil, gasoline, sunlight, and nuclei of uranium-235. Compare low-quality energy. 

Identified resources Deposits of a particular mineral-bearing material of which the location, quantity, and quality are known or have been estimated from direct geological evidence and measurements. Compare undiscovered resources.

kerogen Solid, waxy mixture of hydrocarbons found in oil shale rock. Heating the rock to high temperatures causes the kerogen to vaporize. The vapor is condensed, purified, and then sent to a refinery to produce gasoline, heating oil, and other products. See also oil shale, shale oil. 

life cycle cost Initial cost plus lifetime operating costs of an economic good. Compare full cost.

liquefied natural gas (LNG) Natural gas converted to liquid form by cooling to a very low temperature.

Liquefied petroleum gas (LPG) Mixture of liquefied propane (C3H8) and butane (C4H10) gas removed from natural gas and used as a fuel.

LPG See liquefied petroleum gas. 

magma Molten rock below the earth's surface. 

meltdown Melting of the core of a nuclear reactor. 

mineral resource Concentration of naturally occurring solid, liquid, or gaseous material in or on the earth's crust in a form and amount such that extracting and converting it into useful materials or items is currently or potentially profitable. Mineral resources are classified as metallic (such as iron and tin ores) or nonmetallic (such as fossil fuels, sand, and salt).

Mountaintop removal Type of surface mining that uses explosives, massive shovels, and even larger machinery called draglines to remove the top of a mountain to expose seams of coal underneath a mountain. Compare area strip mining, contour strip mining. 

natural gas Underground deposits of gases consisting of 50-90% by weight methane gas (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C3H8) and butane (C4H10). 

net energy Total amount of useful energy available from an energy resource or energy system over its lifetime, minus the amount of energy (1) used (the first law of thermodynamics), (2) automatically wasted (the second law of thermodynamics), and (3) unnecessarily wasted in finding, processing, concentrating, and transporting it to users. 

Nonrenewable resource Resource that exists in a fixed amount (stock) in various places in the earth's crust and has the potential for renewal by geological, physical, and chemical processes taking place over hundreds of millions to billions of years. Examples are copper, aluminum, coal, and oil. We classify these resources as exhaustible because we are extracting and using them at a much faster rate than they were formed. Compare renewable resource. 

nuclear energy Energy released when atomic nuclei undergo a nuclear reaction such as the spontaneous emission of radioactivity, nuclear fission, or nuclear fusion.

nuclear fission Nuclear change in which the nuclei of certain isotopes with large mass numbers (such as uranium-235 and plutonium-239) are split apart into lighter nuclei when struck by a neutron. This process releases more neutrons and a large amount of energy. Compare nuclear fusion. 

nuclear fusion Nuclear change in which two nuclei of isotopes of elements with a low mass number (such as hydrogen-2 and hydrogen-3) are forced together at extremely high temperatures until they fuse to form a heavier nucleus (such as helium-4). This process releases a large amount of energy. Compare nuclear fission. 

oil See crude oil.

oil shale Fine-grained rock containing various amounts of kerogen, a solid, waxy mixture of hydrocarbon compounds. Heating the rock to high temperatures converts the kerogen into a vapor that can be condensed to form a slow-flowing heavy oil called shale oil. See kerogen, shale oil. 

open-pit mining Removing minerals such as gravel, sand, and metal ores by digging them out of the earth's surface and leaving an open pit. Compare area strip mining, contour strip mining, dredging, mountaintop removal, subsurface mining.

ore Part of a metal-yielding material that can be economically and legally extracted at a given time. An ore typically contains two parts: the ore mineral, which contains the desired metal, and waste mineral material (gangue). 

other resources Identified and undiscovered resources not classified as reserves. Compare identified resources, reserves, undiscovered resources. 

overburden Layer of soil and rock overlying a mineral deposit. Surface mining removes this layer. 

petrochemicals Chemicals obtained by refining (distilling) crude oil. They are used as raw materials in manufacturing most industrial chemicals, fertilizers, pesticides, plastics, synthetic fibers, paints, medicines, and many other products.

petroleum See crude oil. 

precipitation Water in the form of rain, sleet, hail, and snow that falls from the atmosphere onto the land and bodies of water. 

reserve-toproduction ratio Number of years reserves of a particular nonrenewable mineral will last at current annual production rates. See reserves. 

reserves Resources that have been identified and from which a usable mineral can be extracted profitably at present prices with current mining technology. See identified resources, undiscovered resources.

shale oil Slow-flowing, dark brown, heavy oil obtained when kerogen in oil shale is vaporized at high temperatures and then condensed. Shale oil can be refined to yield gasoline, heating oil, and other petroleum products. See kerogen, oil shale. 

smelting Process in which a desired metal is separated from the other elements in an ore mineral.

spoils Unwanted rock and other waste materials produced when a material is removed from the earth's surface or subsurface by mining, dredging, quarrying, and excavation. 

strip mining Form of surface mining in which bulldozers, power shovels, or stripping wheels remove large chunks of the earth's surface in strips. See area strip mining, contour strip mining, surface mining. Compare subsurface mining. 

subsurface mining Extraction of a metal ore or fuel resource such as coal from a deep underground deposit. Compare surface mining.

surface mining Removing soil, subsoil, and other strata and then extracting a mineral deposit found fairly close to the earth's surface. See area strip mining, contour strip mining, mountaintop removal, open-pit mining. Compare subsurface mining. 

synfuels Synthetic gaseous and liquid fuels produced from solid coal or sources other than natural gas or crude oil. 

synthetic natural gas (SNG) Gaseous fuel containing mostly methane produced from solid coal. 

tailings Rock and other waste materials removed as impurities when waste mineral material is separated from the metal in an ore. 

tar sand Deposit of a mixture of clay, sand, water, and varying amounts of a tarlike heavy oil known as bitumen. Bitumen can be extracted from tar sand by heating. It is then purified and upgraded to synthetic crude oil. See bitumen.

Undiscovered resources Potential supplies of a particular mineral resource, believed to exist because of geologic knowledge and theory, although specific locations, quality, and amounts are unknown. Compare identified resources, reserves.