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Gem
Stones
Gem stones are used
for personal adornment and ornamental purposes. A perfect gem stone should be transparent,
beautiful to look at in colour, durable, rare, costly and possess good lustre and high
refractive index. Such stones are called precious stones. Those which are common and cheap and
those lacking any of the above said qualities are treated as semi-precious stones.
Diamond, emerald, ruby, sapphire and opal
are the important precious stones.
The important semi-precious stones are
topaz, aquamarine, spinel, garnet, tourmaline, peridot, zircon, chrysoberyl, quartz,
feldspar,jade, lapis-lazuli, agate and carnelian.
Various semi-precious stones are
displayed.
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Amethyst
Amethyst is a purple or violet variety of quartz. Its colour is probably due to
manganese dioxide. It is used as a semi-precious stone. Amethyst crystals are usually found in
hollow cavities.
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Agate
Agate is a banded variety of chalcedony. The
bands may be straight or zigzag. The colour of the bands are usually grey and white and they
can be artificially coloured. |
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Economic Geology