Pictures
courtesy of Roger Weller
Tiger's
eye (tigers eye, tiger eye, tiger iron) is a member of the quartz group that
contains
oriented fibres of crocidolite that have been replaced by silica. It is one of
the chatoyant gemstones.
Tiger’s eye typically has lustrous
alternating yellow or brown bands. It is a classic example of
pseudomorphous replacement. The gems are usually cut en cabochon in order to
best display their
chatoyancy.
Chatoyancy
is optical reflectance seen in certain gemstones. Derived from the French,
meaning "cat's eye," chatoyancy is from the fibrous structure of a
material, like that found in tiger’s
eye quartz. The effect of chatoyancy is
much like the sheen off a spool of silk; the mobile, wavering
reflection always being perpendicular to the direction of the fibres. For a gemstone to show this
effect it must be en cabochon, with the fibers or fibrous structures parallel
to the base of the
finished stone.
Often times because of their names the mineral
Chrysoberyl or cat’s eye is often confused
with tiger’s eye. However, Crysoberyl is
a beryllium aluminum oxide, which produces the
gemstones alexandrite and cat's - eye.
It's tabular crystals (orthorhombic system) are transparent
to translucent, yellowish green to green or brown, and have a vitreous luster.
Common chrysoberyl
occurs as crystals or loose, rounded grains in granitic pegmatites, and in
metamorphic rocks such
as schist and gneiss. Cat’s eye is an expensive form of chrysoberyl. When polished as cabochons,
these stones exhibit a narrow band of concentrated light along the width of the
gem. This effect,
known as cat's eye effect,
is caused by inclusions of fine, slender parallel fibers in the gem. The cat's
eye variety may be called "cat's eye", cat's eye, "precious
cat's eye", "oriental
cat's eye", "catseye",
or "chrysoberyl cat's eye". Many other gems also exhibit a cat's eye
effect, but only chrysoberyl's
cat's eye enjoys the privilege of having the name "cat's eye". (All
other gems that exhibit a cat's eye
effect must have the gem name preceding, such as "quartz cat's eye",
whereas chrysoberyl's cat's
eye is known simply as "cat's eye".)
Tiger’s Eye Cabochons
Pictures courtesy of Roger Weller
Cat’s Eye Cabochon
http://www.egemstones.com/catseye.html
Characteristics of Tiger’s Eye
http://www.bernardine.com/gemstones/tigers-eye.htm
Color: Brownish
yellow to reddish
Species: Quartz
Chemical
composition: SiO2
Crystal
system: Hexagonal
Hardness: (Mohs scale) 7
Specific
gravity: 2,66 ±0,20
Refractive
index: 1,544 -1,553
Birefringence: 0,009
Optical
character: Uniaxial +
Tiger’s Eye
Occurrence
Tiger's eye is mined in Western
Australia, South Africa, USA, Canada, India, Namibia, and
Burma and the United States. Although
tiger’s eye is found in many countries around the world,
it is believed that the most beautiful tiger’s is found in Africa.
Carved tiger’s eye from Africa
