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What is Gemstone
?
Gem 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 gems are beauty, rarity, and durability.
The beauty of a gem depends primarily on its optical properties,
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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.
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