Pearl

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Contents

Description

A smooth, opaque, iridescent gem formed as a multilayered nacre deposit around foreign matter embedded in the shells of mollusks. Nacre is composed of aragonite crystals bound together with conchiolin. The nacre is built up in thin, concentric layers that grow at rates of less than a millimeter per year. Large, natural pearls a rarity with the largest known pearl weighing 93 grams. The shape of the pearl depends on the shape of the embedded inclusion so most natural pearls are not spherical. Salt-water pearls, also called Oriental pearls, are found in the Persian Gulf, Gulf on Mannar, Myanmar, Tahiti, Borneo, New Guinea, Venezuela, and Australia. Since 1920, pearls have been cultured commercially.

See also pearl, cultured, and pearl, freshwater.

Synonyms and Related Terms

pearls; natural pearls; Oriental pearls; perle (Dan., Fr.); Perle (Deut.); perla (Esp.); parel (Ned.); pérola (Port.); parel (Ned.)

Other Properties

Specific gravity for natural and Oriental pearls = 2.68-2.74; for cultured pearls = 2.70-2.79; and for freshwater pearls = 2.68

Texture: slightly rough

Luster: pearly (iridescent)

Color: white, pale yellow, pink, gray, brown, black

Most exhibit a sky -blue color fluorescence

Mohs Hardness 3 - 4
Density 2.68-2.4

Hazards and Safety

Easily damaged by acids. Deteriorates at low humidities. Easily scratched. May be discolored by soap or skin oil.

Authority

  • Oppi Untracht, Jewelry Concepts and Technology, Doubleday & Co., Inc., New York City, 1985 Comment: specific gravity for Oriental pearls = 2.68-2.74, cultured = 2.70-2.79, freshwater pearls = 2.68; average hardness = Mohs 3-4; double refraction = 1.57
  • Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 1982
  • Encyclopedia Britannica, http://www.britannica.com Comment: "pearl." Encyclopædia Britannica. 2004. Encyclopædia Britannica Premium Service. 23 Dec. 2004 .
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971
  • Caring for your Collections, Arthur W Schulz (ed.), Harry N. Abrams, Inc. , New York, 1992

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