Cochise College Student Papers in Geology
Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
wellerr@cochise.edu
Quartz Family Gemstones-by
Audrey LaClair
Tigereye or Tiger's Eye
Tiger's eye starts out as a blue mineral called crocidolite, which happens to be
fibrous. Crocidolite is actually what we know as asbestos. It starts to
transform into tigereye when quartz starts becoming embedded in the crocidolite.
When this happens, one of two gemstones is formed. It is either Tiger's eye or
Hawk's eye. When this happens, the asbestos dissolves completely. The quartz
then changes into fibrous formations and retains the blue color from the
crocidolite. Because of this, it creates parallel lines in the gem that creates
the light shift and movement; which is also known as chatoyancy. The gleam that
rolls across the surface is like the eyes of a cat. Geological conditions then
change the color of tigereye into a deep yellow, brown, green, and rarely
blue. It can turn red by heating, either naturally or artificially.
photo by R.Weller
"The gems
are usually cut en cabochon in order to best
display their chatoyancy. Red stones are brought about through gentle heat
treatment. Honey-coloured stones have been used to imitate the much higher
valued cat's eye chrysoberyl (cymophane), but
the overall effect is unconvincing" (
http://en.wikipedia.org/wiki/Tiger's_eye).
Tigereye is
most frequently found in South Africa. Unfortunately, on May 10, 1968, Carol de
Wet announced an embargo on the exportation of rough tigereye. This led to all
rough export being eliminated by May of 1971. This was to create a South
African monopoly on the finished tigereye. Now, all rough tigereye is being
smuggled out of the country in huge quantities instead of being legally
exported. This rough tigereye is finished in other countries and then sold out
as a profit. Tiger's eye can also be found in the USA, Canada, Western
Australia, Namibia, Burma, and India.
photo by R.Weller
"Tiger's Eye is the Planetary stone for Gemini (May 21-Jun. 20) and the accepted gem for the ninth wedding anniversary" ( http://www.bernardine.com/gemstones/tigers-eye.htm ).
There are many legends that say if one wears tiger's eye, it will be beneficial for both spiritual well being and health. Another legend says it is great for business, aids to achieving clarity, and a psychic protector.
photo by R.Weller
Physical Properties
Color - various shades of golden or honey yellow and
various brown hues, typically roughly striped
H. (effective hardness) 6.5 - 7
S.G. ~ 2.65 - 2.9.
Light transmission - subtranslucent to opaque
Luster - a silky sheen that is improved markedly by cutting and polishing
Breakage - subconchoidal to irregular
From ( http://www.cst.cmich.edu/users/dietr1rv/hawkseye.htm ).
References:
http://www.minerals-n-more.com/Tiger_Eye_Info.html
http://en.wikipedia.org/wiki/Tiger's_eye
http://www.cst.cmich.edu/users/dietr1rv/hawkseye.htm
http://www.bernardine.com/gemstones/tigers-eye.htm
http://www.lapidaryjournal.com/feature/jul00str.cfm
http://www.minerals-n-more.com/Tiger_Eye_Info.html