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sapphire
(Encyclopedia)sapphire, precious stone. A transparent blue corundum, it is classified among the most valuable of gems. Sapphires are found chiefly in Madagascar, Sri Lanka, and Myanmar and also in Thailand, Tanzani...corundum
(Encyclopedia)corundum kərŭnˈdəm [key], mineral, aluminum oxide, Al2O3. The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in mass...Ratnapura
(Encyclopedia)Ratnapura rŭtˈnəpo͝orə [key] [Sinhalese,=city of gems], town (1995 est. pop. 46,000), SW Sri Lanka. Located in a rubber- and rice-producing area, Ratnapura is Sri Lanka's major precious-stone cen...lapis lazuli
(Encyclopedia)lapis lazuli lăpˈĭs lăzˈo͝olē [key], gem, deep blue, violet, or greenish blue in color and usually flecked with yellow iron pyrites. It is composed of lazurite, a complex sodium aluminum silica...tanzanite
(Encyclopedia)tanzanite tănzănˈīt [key], beautiful gemstone discovered in 1967 in the Umba Valley near the Usambara Mts. in Tanzania, a precious variety of the mineral zoisite, a calcium aluminum silicate. Zois...amethyst
(Encyclopedia)amethyst ămˈəthĭst [key] [Gr.,=non-drunkenness], variety of quartz, violet to purple in color, used as a gem. It is the most highly valued of the semiprecious quartzes. It is associated with a num...tourmaline
(Encyclopedia)tourmaline to͝orˈməlĭn, –lēn [key], complex borosilicate mineral with varying amounts of aluminum, iron, magnesium, sodium, lithium, potassium, and sometimes other elements, used as a gem. It o...month
(Encyclopedia)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 month a...bearing
(Encyclopedia)bearing, machine part designed to reduce friction between moving parts or to support moving loads. There are two main kinds of bearings: the antifriction type, such as the roller bearing and the ball ...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...Browse by Subject
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