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Grades
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There
are three varieties of chrysoberyl: (1) The yellow-green variety is
known as 'chrysolite' which is a name also applied to olivine. There is
also a chance of mistaking chrysoberyl without chatoyancy for olivine
or chrysolite, whose hardness is much lower than that of chrysoberyl.
(2) Cat's eye is the chatoyant, opalescent variety which is also known
as cymophane with a silky lustre and green colour. This stone when cut
en cabochon has an attractive band of light on the stone, which changes
on rotation. The play of light in a certain direction amounts to a
phosphorescent brilliance and is found in various colours. This
chatoyancy is only an accidental character. This is a popular stone and
the best quality stones fetch good prices.
This
has been called by the Hindus as ' Vaidooryam', and has also been
classed into 4 castes as in the case of other precious stones: (1)
Brahmin—white cat's eye with a gleam of blue, (2) Kshatriya—white cat's
eye with a gleam of red, (3) Vaisya—yellow cat's eye with a blue
lustre, (4) Sudra—purely blue cat's eye. The cat's eye which sparkles
beautifully is also known as 'sutra'. It has also good qualities and
the usual defects. The popular colours are apple green and dark olive.
When held against the light, the stone resembles the contracted pupil
of a cat. It has double refraction and acquires electricity by friction.
Alexandrite
is another interesting variety, with a dark green colour by daylight
and deep red by artificial light. It is also strangely
pleochroic—chromium is supposed to be the cause of colour in
Alexandrite.
Mode of Cutting
The mode of cutting adopted is en cabochon. It is cut on a copper wheel with emery and polished with Tripoli.
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