Columbia Encyclopedia

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gem, ornamental mineral or organic substance

(Encyclopedia)gem, commonly, a mineral or organic substance, cut and polished and used as an ornament. Gems also are used as seals (items of assurance) and as talismans (good-luck charms). For birthstones, see mont...

mineral

(Encyclopedia)mineral, inorganic substance occurring in nature, having a characteristic and homogeneous chemical composition, definite physical properties, and, usually, a definite crystalline form. A few of the mi...

pearl, gem

(Encyclopedia)pearl, hard, rounded secretion formed inside the shell of certain mollusks, used as a gem. It is secreted by the epithelial cells of the mantle, a curtain of tissue between the shell and body mass, an...

substance

(Encyclopedia)substance, in philosophy, term used to denote the changeless substratum presumed in some philosophies to be present in all being. Aristotle defined substance as that which possesses attributes but is ...

brasses, ornamental

(Encyclopedia)brasses, ornamental. Brass, a copper-zinc alloy produced since imperial Roman times, is closely associated in art with bronze, a copper-tin alloy (see bronze sculpture). Brass was generally fashioned ...

organic food

(Encyclopedia)organic food, food raised without chemicals and processed without additives. Under standards adopted by the U.S. Agriculture Dept. (USDA) in 2000 and fully effective in 2002, synthetic fertilizers and...

organic farming

(Encyclopedia)organic farming, the practice of growing plants—especially for fruits and vegetables, but for ornamentals as well—without the use of synthetic pesticides, herbicides, and fertilizers, or of raisin...

GEM, acronym for ground-effect machine

(Encyclopedia)GEM: see air-cushion vehicle.

mineral water

(Encyclopedia)mineral water, spring water containing various mineral salts, especially the carbonates, chlorides, phosphates, silicates, sulfides, and sulfates of calcium, iron, lithium, magnesium, potassium, sodiu...

organic chemistry

(Encyclopedia)organic chemistry, branch of chemistry dealing with the compounds of carbon. While it is only the fourteenth most common element on earth, carbon forms by far the greatest number of different compound...