from the palace of King Thibaw at Mandalay. They are now exhibited in the Indian Museum in London.
Synthetic
rubies and sapphires are also sold in large quantities for gem and
industrial purposes, because they are relatively inexpensive and show
more uniform characters, and are given a range of very attractive
colors. The stones are identical in their characters. They are
considered inferior, because they could be produced cheap and have
caused severe competition in the trade.
Chapter XIII
THE SPINEL GROUP
Introduction
SPINEL
was also known from ancient times along with the ruby and was classed
with the ruby by mistake. It was known as spinel ruby or ruby spinel,
which has a fine lively red with a cinnamon tint about it, but is
inferior to the true ruby in brilliance. Spinel and ruby are always
associated with the gem gravels. The gem rubies, sapphire and spinel
could easily be identified as spinel is softer, lighter, isotropic and
non-pleochroic. The Indian names were Saugandhika, classed as Vaisya ruby, and Mansa-khanda—Balas
ruby as Sudra ruby, and these were included in the rubies, though by
chemical composition and crystallization they are entirely separate.
Physical Properties
It
crystallizes in the cubic system, octahedron being the common form.
Twinning is also frequent, two octahedra having grown back to back in
symmetrical position. It is known as spinel twin and other minerals
also show similar twinning. Cleavage is imperfect and octahedral;
fracture
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