ALEXANDRITE
So
named after Alexander II. of Russia, being discovered in his dominions
on the day he attained his majority (1830), its dichroism exhibits the
Russian colors.
It
is a variety of chrysoberyl, of which the Oriental cat's-eye is one,
and is found in Russia, Ceylon, Brazil, and occasionally in the United
States. Some have been found in Ceylon which exhibit a cat's-eye
chatoyancy.
Crystallization trimetric. Crystals, modified rectangular prisms, usually double six-sided, sometimes thick, often tabular.
Hardness, 8.5. Specific gravity, 3.5 to 3.8.
Lustre vitreous; transparent to translucent.
Cleavage imperfect; fracture conchoidal.
Doubly
refractive (index, 1.756 and 1.747) ; strongly di-chroic, sometimes
trichroic; twin colors, green and yellow or green and red; positively
electric.
It is composed of alumina, 79; glucina, 18; iron and chromic oxide, etc., 3.
Melts with borax, but is infusible and unaltered before the blow-pipe, and is unaffected by acids.
By
day the color is a light to dark bottle-green, but by artificial light
it becomes purplish pink to columbine-red, rarely ruby-red. The streak
is uncolored.
The rough is generally so full of structural defects, crevices, etc., as to make it unfit for use as a gem.
The
ideal gem, a bright tourmaline-green by day, and ruby-red at night, is
very rare, one or the other color, often both, being weak. Usually
step-cut.
Symbolizes undying devotion.
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