Tuesday, September 20, 2011

Tiger's Eye, Tiger Iron or Hawk's Eye - you select your choice !

If these three gemstones were placed in front of you, could you pick them out immediately? I hope so by the time you finish reading this Blog.

Tiger’s Eye is a chatoyant gemstone that belongs to the Quartz family. It is normally a metamorphic rock which is yellow to red-brown in color with a silky luster. Chatoyancy is a changing in the luster or color of a gemstone as light is reflected within the thin parallel fibrous bands. The fibrous structure of the material is what causes this effect to happen. Tiger's Eye gemstones are normally cut into various cabochon shapes to best display their chatoyancy. Tiger's Eye can also show a Cat's Eye effect.

Tiger's eye is derived from Crocidolite (a mineral comprised of iron and sodium) which has been oxidized to a golden brown from its original blue color and the Crocidolite has been totally replaced by Quartz. An incomplete silicified process producing a blue variant is known as Hawk’s eye.

Even though the iron and sodium dissolves when the Quartz becomes imbedded between the fibers of Crocidolite, there are traces of hydrated oxide of iron that are left between the Quartz and Crocidolite, thus creating the golden color that is common to the Tiger's Eye gemstone. How golden brown, red, blue or green the Tiger's Eye and Hawk's Eye ends up is determined by how much of these varying amounts of hydrated minerals are deposited. The rarer blue Hawk's Eye will have only the slightest amounts. Tiger's Eye is also called a Cat’s Eye Quartz when the color is greenish grey. It is called Tiger’s Eye Cat Eye when the brown stone reflects a golden yellow stripe and if the stone is bluish or blue gray, then it is known as Hawk's Eye Cat Eye. The rare mahogany or any redish colored stones are known as Ox Eye or Bull's Eye.

Tiger's Eye is also a pseudomorph. Pseudomorphs form when one mineral replaces another. Since Tiger's Eye is a Quartz replacement of Crocidolite, therefore it is a pseudomorph of Quartz after Crocidolite. The same thing happen when Quartz replaces wood to produce Petrified Wood. Tiger's Eye is also considered as one of the most popular chatoyant gemstones.

Now we throw in a confusion factor for identification. Tiger Iron is a composite gemstone of black Hematite, red Jasper and Tiger's Eye. It has rippled wavy bands of color often which resemble a scenic view. It usually has a greenish cast with shades of golden yellow, brown and reds. Marra Mamba is a form of Tiger Iron that was found only in a specific area of Australia near Mount Brockman. It is a very rare type of Tiger Iron that contains shades of green, red, blue and yellow. Since the area has been mined out for many years, very little of the "true" Marra Mamba is available in todays markets. If you want to see some, find a good collector or a museum that might have some.

Tiger’s Eye is often heat treated in which any changes are permanent, therefore no extra care is needed, but just like any other gemstone it should be protected from sharp blows, heavy scratches and large temperature changes. Quartz dust can be hazardous to breathe according to several recent research studies. Since the fibrous mineral in most Tiger's Eye has been completely replaced by Quartz, it is best to take adequate precautions to avoid breathing any of the dust when cutting or polishing Tiger's Eye, or any oher Quartz stone.

The fibers in Tiger's Eye are very thin and may only be an inch or two long. Most are only 0.001 millimeters, in diameter. Since Tiger’s Eye normally has bend or twisted fibers, sawing can be tricky and cuts must exactly parallel to the length of the fibers in order to get the full chatoyant effect. You will end up with a lifeless, dark brown to black worthless stone if the saw cut is perpendicular to the fibers. Very careful cutting and polishing is required to line all the fibers up to get a true cat-eye effect.

Red Tiger's Eye is not a natural occurrence in most cases. It is usually a result of deliberate heating. Honey-colored Tiger's Eye have been used to imitate much higher valued Cat’s Eye Chrysoberyl. The most common man made imitation of Tiger's Eye is an artificial fiberoptic glass and/or resin that is produced in a wide range of unusual colors.

Tiger’s Eye commonly comes from South Africa but also can be found in Burma, Australia, the United States and India.