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	gem 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 month . Properties of Gems The qualities sought in gems are beauty, rarity, and durability. The beauty... Read more
	James Tassie James Tassie 1735-99, Scottish gem engraver and modeler. At first a stonemason, he went to Dublin, where he assisted the gem engraver Dr. Henry Quin. With him Tassie invented an especially hard and fine-textured white enamel for making replicas of gems. In 1766 he went to London, where he... Read more
	bloodstone bloodstone or heliotrope, green chalcedony spotted with red, used as a gem stone. It is found in India, the United States, Brazil, and Australia.... Read more
	Pearl (oyster) 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, and is deposited in successive layers around an irritating object—usually a parasite in the case... Read more
	jasper jasper opaque, impure cryptocrystalline quartz , usually red, but also yellow, green, and grayish blue. It is used as a gem. Ribbon jasper has the colors in stripes.... Read more
	carnelian carnelian or cornelian , variety of red chalcedony , used as a gem. It is distinguished from sard by the shade of red, carnelian being bright red and sard brownish. The red coloring is apparently caused by iron oxide.... Read more
	corundum corundum , mineral, aluminum oxide, Al 2 O 3 . The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in masses. It is transparent to opaque and has a vitreous to adamantine luster. The transparent gem varieties are... Read more
	emerald emerald the green variety of beryl , of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The emerald was highly esteemed in antiquity; the stones were used for ornaments in early Egypt where some of... Read more
	Paper Clip Paper Clip Background The paper clip is a nearly ubiquitous device, used worldwide to temporally hold papers together. The technology for manufacturing paper clips evolved in the early years of the twentieth century, and has remained virtually unchanged since the 1930s.... Read more
	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... Read more