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Platte

(Encyclopedia)Platte, river, c.310 mi (500 km) long, formed by the confluence of the North Platte (680 mi/1,090 km long) and South Platte (430 m/690 km) rivers at North Platte, Neb. It flows generally E across S Ne...

periwinkle, in zoology

(Encyclopedia)periwinkle, any of a group of marine gastropod mollusks having conical, spiral shells. Periwinkles feed on algae and seaweed. They are found at the water's edge; out of water, they resist drying by cl...

calcium carbonate

(Encyclopedia)calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. Calci...

biosphere

(Encyclopedia)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 e...

geode

(Encyclopedia)geode jēˈōd [key], hollow, globular rock nodule ranging in diameter from 1 to 12 in. (2.54–30.5 cm) or more. Most geodes are partly filled with mineral matter; they have a thin layer of chalcedon...

sedge

(Encyclopedia)sedge, common name for members of the Cyperaceae, a family of grasslike and rushlike herbs found in all parts of the world, especially in marshes of subarctic and temperate zones. The name sedge is al...

Salton Sea

(Encyclopedia)Salton Sea sôlˈtən [key], saline lake, 370 sq mi (958 sq km), northern part of the Imperial Valley, SE Calif.; 232 ft (71 m) below sea level. The area was anciently the northern part of the Gulf of...

sodium carbonate

(Encyclopedia)sodium carbonate, chemical compound, Na2CO3, soluble in water and very slightly soluble in alcohol. Pure sodium carbonate is a white, odorless powder that absorbs moisture from the air, has an alkalin...

mirage

(Encyclopedia)mirage mĭräzhˈ [key], atmospheric optical illusion in which an observer sees in the distance a nonexistent body of water or an image, sometimes distorted, of some object or of a complete scene. Exa...

air conditioning

(Encyclopedia)CE5 Cross section of air conditioning unit. air conditioning, mechanical process for controlling the humidity, temperature, cleanliness, and circulation of air in buildings and rooms. Indoor air i...