|
Natural
GemStone is actually a mineral or an organic substance which is cut, polished and used as an ornament. Gems are also used as seals (items of assurance) and as talismans (good-luck charms). However modern age has found numerous uses of Gems in different fields.
The qualities sought in Natural gemstones are beauty, rarity, and durability. The beauty of a gemstone depends primarily on its optical properties, which impart its luster, fire, and color. The durability depends on hardness and resistance to cleavage or fracture. The physical properties by which gems are distinguished from each other are form of the crystal, index of refraction of light, hardness, presence or absence of cleavage, type of fracture
(conchoidal, even, or uneven) in stones without cleavage, specific gravity, color, streak (color of the powder as determined by rubbing it over white, unglazed porcelain), luster (appearance of the surface in reflected light-adamantine, vitreous, resinous, greasy, silky, or pearly), and transparency. Minor properties that serve to identify some stones are chatoyancy (changeable luster or color under undulating light), opalescence, asterism
(starlike sparkling), play of color, fluorescence, phosphorescence, iridescence, and electrical properties. The unit of weight used for gemstones is the metric carat. One carat is equal to 200 mg.
|
