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iridescence
iridescence , exhibition of rainbowlike colors on a surface. It usually results from interference when light composed of different wavelengths is reflected from the superficial layers of organic or inorganic substances, e.g., minerals, mother-of-pearl, and the feathers of birds. Iridescence greatl...
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quartzite
quartzite usually metamorphic rock composed of firmly cemented quartz grains. Most often it is white, light gray, yellowish, or light brown, but is sometimes colored blue, green, purple, or black by included minerals. It results from the metamorphism of pure quartz sandstone . It is most easily ...
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tetany
tetany , condition of mineral imbalance in the body that results in severe muscle spasms. Tetany occurs when the concentration of calcium ions (Ca ++ ) in extracellular fluids such as plasma falls below normal. The nervous system becomes increasingly excitable, and nerves discharge spontaneously, se...
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stratification
stratification (Lat.,=made in layers), layered structure formed by the deposition of sedimentary rocks . Changes between strata are interpreted as the result of fluctuations in the intensity and persistence of the depositional agent, e.g., currents, wind, or waves, or in changes in the source of t...
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biosphere
biosphere irregularly shaped envelope of the earth's air, water, and land encompassing the heights and depths at which living things exist. The biosphere is a closed and self-regulating system (see ecology ), sustained by grand-scale cycles of energy and of materials—in particular, carbon, o...
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Alaska North Slope
Alaska North Slope or Arctic North Slope, region, N Alaska, sloping from the Brooks Range N to the Arctic Ocean. In 1968 large petroleum reserves were found in the Prudhoe Bay area. In 1977 the 800-mi (1,287 km) Trans-Alaska pipeline was completed to carry oil S to the port of Valdez, on the ...
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coal mining
coal mining physical extraction of coal resources to yield coal; also, the business of exploring for, developing, mining, and transporting coal in any form. Strip mining is the process in which the overburden (earth and rock material overlying the coal) is removed to expose a coal seam or coal bed....
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divining rod
divining rod or dowser, stick used in searching for underground water or minerals. This form of divination is still in common use in many parts of the world. The instrument is typically a forked twig. The operator holds the forked ends of the twig close to his body, with the stem pointing forwa...
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heat exhaustion
heat exhaustion condition caused by overexposure to sunlight or another heat source and resulting in dehydration and salt depletion, also known as heat prostration. The symptoms are severe headaches, weakness, dizziness, blurred vision, and sometimes unconsciousness. However, the body temperature i...
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Lobengula
Lobengula , c.1833-94, king of Matabeleland (now in Zimbabwe). After succeeding his father (1870), he tried to turn aside the approaches of European colonizers. In 1888, however, under pressure from Cecil Rhodes , he ceded his mineral rights in exchange for small payment, and Rhodes used those conc...
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