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Columbia Encyclopedia entry: garnet
Garnet, name applied to a group of isomorphic minerals crystallizing in the cubic system. They are used chiefly as gems and as abrasives (as in garnet paper). The garnets are double silicates; one of the metallic elements is calcium, magnesium, ferrous iron, or manganese and the other aluminum, ferric iron, or chromium. Six varieties (of which there are also intermediate forms) are distinguished according to composition—grossularite (calcium-aluminum), pyrope (magnesium-aluminum), spessartite (manganese-aluminum), almandite (iron-aluminum), andradite (calcium-iron), and uvarovite (calcium-chromium). Grossularite occurs commonly in a red, green, yellow, or brown shade, depending on the impurities; if pure it would be colorless. The yellow and brown stones, coming chiefly from Sri Lanka, are used as gems under the names essonite (or hessonite) and cinnamon stone; sometimes they are miscalled hyacinth. Grossularite is found also in the Transvaal, in Mexico, and in Oregon. The most popular variety of garnet is the ruby-red pyrope from Bohemia, S Africa, and Arizona, sold as Cape ruby and Arizona ruby. Rhodolite, a mixture of pyrope and almandite from North Carolina, is rose-red or purple. Spessartite, a brown to brownish-red garnet from Bavaria, Sri Lanka, and parts of the United States, is seldom used for jewelry. Deep red, transparent almandite is the carbuncle; it was formerly a very popular gem. Almandites come chiefly from Brazil, India, and Sri Lanka; Australia and parts of the United States are also important sources. Andradite, a very common variety, is usually some shade of red, black, brown, yellow, or green. Gem varieties include topazolite, similar in color and transparency to topaz; demantoid, a green variety with a high dispersion and adamantine luster, sometimes miscalled olivine and Uralian emerald; and black melanite. Demantoid is found in the Urals, and the other andradites come chiefly from Europe and the United States. Uvarovite, an emerald-green variety from Russia and Finland, is rarely suitable for gem use. Garnet occurs in many different kinds of rocks—grossularite, in metamorphosed impure limestones; pyrope, in basic igneous rocks; spessartite, in granite rocks; almandite, in schists and other metamorphic rocks as well as in igneous rocks; andradite, in serpentine; and uvarovite, chiefly in serpentine.
Wikipedia search results for: Garnet
From Wikipedia, the free encyclopedia
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus, possibly a reference to the Punica granatum, a plant with red seeds similar in shape, size, and color to some garnet crystals. Six common species of garnet are recognized by their chemical composition. They are pyrope, almandine, spessartine, grossular, uvarovite and andradite. The garnets make up two solid solution series: 1. pyrope-almandine-spessarite and 2. uvarovite-grossular-andradite. Garnets species...more »
Columbia Encyclopedia search results: garnet
Results 1 - 10  of 14
  • Garnet, Henry Highland

    Garnet, Henry Highland, 1815–82, American abolitionist clergyman, b. Kent co., Md. Born a slave, he escaped in 1824 and was educated at the Oneida Institute, Whitesboro, N.Y. He was an eloquen...

  • Wolseley, Garnet Joseph Wolseley, 1st Viscount

    Wolseley, Garnet Joseph Wolseley, 1st Viscount, 1833–1913, British field marshal. He fought in Burma (present-day Myanmar; 1852–53), the Crimea (1854–56), India (1857–58), and China (1860), an...

  • Garnett, Henry

    Garnett or Garnet, Henry, 1555?–1606, English Jesuit. He was converted to Roman Catholicism and in 1575 became a Jesuit. After some years on the Continent he returned as a missionary to Englan...

  • Kuprin, Aleksandr Ivanovich

    Kuprin, Aleksandr Ivanovich, 1870–1938, Russian novelist and short-story writer. Kuprin was an army officer for several years before he resigned to pursue a writing career. He won fame with Th...

  • Swakopmund

    Swakopmund, municipality (1991 pop. 17,681), W Namibia, on the Atlantic at mouth of Swakop River. A rail terminus and seaside resort surrounded by the Namib desert, the town was originally a p...

  • gneiss

    Gneiss, coarse-grained, imperfectly foliated, or layered, metamorphic rock. Gneiss is characterized by alternating light and dark bands differing in mineral composition and having coarser grai...

  • month

    Month, in chronology, the conventional period of a lunation, i.e., passage of the moon through all its phases. It is usually computed at approximately 29 or 30 days. For the computation of the...

  • pitta

    Pitta, name used to refer to a genus (Pitta) of small, plump, brightly colored birds. The genus, including some twenty-three species, constitutes the whole of the family Pittidae. Known also a...

  • calcium

    Calcium [Lat.,=lime], metallic chemical element; symbol Ca; at. no. 20; at. wt. 40.08; m.p. about 839°C; b.p. 1,484°C; sp. gr. 1.55 at 20°C; valence +2. Calcium is a malleable, ductile, silver...

  • sand

    Sand, rock material occurring in the form of loose, rounded or angular grains, varying in size from .06 mm to 2 mm in diameter, the particles being smaller than those of gravel and larger than...

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