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The Gemstone Tiger Eye
I think the gemstones, Tiger's Eye and Fire Opal. Have probably created
more rock hounds, then you can shake, your proverbial stick at. It is
a well known fact that Raccoons are
attracted to shiny objects. Evidently most human children are too. I know
my little Raccoon eyes were always drawn to the flashy color play of Opal.
Just as intriguing were some giant Tiger Eye stones, owned by my mentor.
They were mixed blue and gold Tiger's Eye. Which produced an ever shifting
play of light.
To this day, even though I have many rare and unusual stones, in my own
store. These are
still two of my favorite stones. I'm not alone in this feeling either.
When groups of children come to our store, more often than not, when their
hands go up for questions. The questions
are about, one or the other, of these two stones.
PHYSICAL PROPERTIES:
Tiger's Eye is a durable quartz composite with the usual quartz hardness
of 7. It begins as
the fibrous blue mineral called crocidolite, which is comprised of iron
& sodium. Most of us known crocidolite as asbestos. The transformation
begins when quartz becomes imbedded between the fibers of crocidolite.
This process will result in one of two gemstones. A blue
stone called Hawk’s Eye or the golden brown stone called Tiger’s Eye.
During the process, the asbestos is completely dissolved. But The quartz
takes on the
fibrous formations and the blue color of crocidolite. This creates
the parallel lines within
the gem which gives it that ever shifting play of light and movement,
the stone is so loved
for. This is also known as chatoyancy. This gleam that rolls across
its surface. Much like
the eyes of a cat.
Even though the iron & sodium dissolve, traces of hydrated oxide of
iron deposit between
the crocidolite and quartz, creating the golden color that is common to
Tiger's Eye. How
much of this hydrated mineral is deposited will determine how Golden brown,
red, green or
blue, Tiger's Eye and Hawk's Eye will be. The rarer blue Hawk’s
Eye will have only the slightest amounts.
The varying amounts of hydrated oxide of iron, actually cause several
colors and mixes of color. When the color is a greenish gary, it is called
cat's-eye quartz. A golden yellow
reflection on a brown stone, is called Tiger's Eye. If the stone is blue
gray or bluish, it's
known as Hawk's Eye. Redish brown, or mahogany colored stones, are known
as
bull's-eye or ox-eye
Tiger's Eye is also a pseudomorph (from the Greek for “false form”). Pseudomorphs
form
when one mineral replaces another. Tiger-eye is a quartz replacement of
crocidolite. Thus it
is a pseudomorph of quartz after crocidolite. The process is similar to
that which takes place when quartz replaces wood to produce petrified
wood.
LOCALITIES:
In my younger days the old timers maintained that Tiger's Eye was only
found in Africa.
Today I find this to be only a half truth. It is true that Tiger Eye's
major commercial source
is Cape Province, South Africa. But There are several locations that have
Tiger's Eye. More
to the point. Tiger's Eye mixed with other materials or Tiger's Eye like
materials. They are
all quartz replacements of fibrous minerals and show some chatoyance.
Unfortunately, On May 10, 1968, Dr. Carol de Wet, then Minister of Mines
of the Republic
of South Africa. Announced an embargo on the exportation of uncut Tiger's
Eye that
gradually eliminated all export of rough Tiger's Eye, by May of 1971.
His intent being
to create a South African monopoly on finished Tiger's Eye gems.
It is said that huge quantities were smuggled out. But smuggling costs
money and the price
of rough increased much faster than the buying public's willingness to
pay. Nowadays, even
at large gem shows, you really have to search long and hard to find any
rough Tiger's Eye. However regular golden Tiger's Eye gemstones, are not
too expensive. On the other hand these stones are mostly just the golden
color. We have some of the older more rare color mixes.
Another rare Tiger's Eye like stone we have, is Binghamite. Binghamite
is composed of
quartz and fibrous silicates with inclusions of goethite and/or hematite.
It is a highly prized gemmy material with a chatoyant luster, similar
to Tiger's Eye. It's is usually red or yellow
and may have black streaks of hemitite and sometimes blocky patches of
white quartz.
It can be a very interesting alternate to Tiger's Eye. It is found in
the Cuyuna Iron Range
of Minnesota. Silkstone is analogous to binghamite but the fibers are
randomly oriented
and it is not so highly prized.”
Australia has a stone called Tiger Iron. Some tiger-iron is all golden
just like the South
African Tiger's Eye and is called Australian Tiger's Eye, by some American
dealers.
Some is more of a mixture, with visible streaks of red jasper. If it's
mostly jasper, some
dealers call it Tiger's Eye Jasper. Some also incorporates silvery gray
hematite. This
variety is called Tiger Iron by pretty much everyone.
Pietersite is a chatoyant, solidified crocidolite asbestos, but its appearance
is quite different because it's been broken into fragments (brecciated,
in mineralogical terms), stirred around, and re-cemented by silica. The
result is a patchwork of shades of blue, yellow, brown, and
red. Pietersite originally found in Namibia. Is now also coming from Henan
Province, China.
We have also seen adds for Golden Chinese Tiger's Eye. The Chinese pietersite
is very
similar to the Namibian one, but it has more red color and distinctive
golden-red combinations.
There are also some materials from California and Arizona that might qualify.
The California type applies to a silica-impregnated, white-to buff-colored,
massive, fibrous tremolite (another asbestos mineral) that was collected
for many years at Iowa Hill in Placer County.
The Arizona variety consists of fibers of chrysotile (also another asbestos
mineral) in serpentine. As a rule neither of these stones are very impressive.
We have heard of other localities. Such as Sri Lanka (Ceylon), India,
Brazil and Burma.
But I haven't seen much information on these localities
HISTORY & FACTS:
The fibers in Tiger's Eye may be an inch or two long and very thin. Most
are only 0.001 millimeters, or 0.000039 inches, in diameter.
Tiger's Eye has a fibrous structure. and sawing can be tricky. Because
nature seldom grows
the fibers straight. They are usually bend or twisted. Cuts must be exactly
parallel to the
length of the fibers to get the full chatoyant effect. If the saw cut
is perpendicular to the
fibers. You end up with a lifeless, dark brown to black stone.
While on the subject of cutting, even though in most tiger-eye the fibrous
mineral has been completely replaced by quartz, recent research has shown
that quartz dust can be hazardous
to breathe. So when working quartz or any stone. Take adequate precautions
to avoid
breathing any of the dust.
In most cases Red Tiger's Eye is not a natural occurrence. It is
usually a result of deliberate heating. Heat treating can be done using
the kitchen oven. First fill a can or some sort of
metal container with sand. To protect the tiger-eye from thermal shock
during heating.
Cover slabs of ordinary, yellowish Tiger's Eye in fine clean silica sand,
at least 3" deep.
You can get this sand at your local lumber yard. It is used for sand blasting.
Place them in
a cold oven and increase the temperature 50°F every hour until it reached
400°F. Then turn
the oven off. Do not open the door. Allow plenty of time for the container
to cool all the way through.
Soon after Tiger Eye's discovery in the late 19th century. Idar-Oberstein
lapidaries
discovered they could bleach tiger-eye to an evenly colored light yellow.
By using either hydrochloric or oxalic acid. When properly oriented and
cut, this material could yield a
sharp cat's-eye stone. Which was more than just a little reminiscent of
“real” cat's-eye. An expensive variety of chrysoberyl.
Tiger's Eye also shows a cat's-eye effect. It just isn't the same color
as the light yellow chrysoberyl. Other gems that show a similar effect
are cat's-eye opal and cat's-eye
tourmaline. Both effects are referred to as chatoyant. "Chatoyant" comes
from the French word for "cat." and these stones do gleam like a cat's
eye.
Tiger's Eye is the anniversary gemstone for the 9th year of marriage.
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Chuck and Virginia Brown
Golden Arts Fine Jewelry
1127 Snake River Ave.
Lewiston, Idaho 83501
1-208-746-1506