Tiger Eye

Tiger Eye
by Bill Gallagher
ok to reproduce in entirety w/credit not for profit

Tiger Eye is a substance of many names and forms.  Pseudomorphic, it is technically considered to be silicified asbestos, or asbestos replaced with silica, although new finds and greater intuitions are indicating that perhaps the rock did not form in the manner which has been previously alluded.   Some say that Tiger's Eye Quartz is a fully silicified form of the mineral Crocidolite, with the varieties of red and blue being caused by varying degrees of silicification, or heat exposure, or both.  One source states that Crocidolite is pseudomorphic chalcedony after another mineral called Riebeckite.  Lately there has been another form on the market called Pietersite which includes blue and gold and figurals not available among the more common varieties of this stone.  As time goes on, it is almost certain that even more odd and usable finds of this stone will manifest.

There is a lot of disagreement concerning the way Tiger's Eye Quartz developed, and because there is, truly, a lot of local variety among the various stones called Tiger Eye, there is certainly room for a variety of formation scenarios as well.  Because many of our so-called discoveries must be constantly reviewed and updated, and because many of our ideals are based on which human is the most underhanded and conniving, ie. the best political goonie, there are those who say that our attempts at figuring things out, things in general, are just a rather amusing form of arrogance and ego, though I am not in agreement with that.  The result of our mental meanderings may be wrong, or only partially right, or even preposterous at times, but its the trying that matters, its the exercise of building good thought patterns which increases our ability to reason and discern correctly.  That is MY opinion, or, dare I say, my belief?

However it may be, this stone type is considered to be a type of Quartz, and it is alternately called Cat's Eye (Greenish grey or green), Hawk's Eye (Blue grey or bluish), and Bull's Eye or Ox Eye Quartz (Mahogany).  Tiger's Eye Quartz is the yellowish brown variety.  Some of the various colors of this quartz can and are created artificially by heat treating, though there is a pretty broad spectrum of colors among rocks closely associated at the various deposits around the world, so heat treating is not really necessary to get any particular color, except perhaps for red. 

One main trait of Tigers Eye is called Chatoyance, that is, the cut and polished examples are chatoyant, or exhibit chatoyance, also known as the Cats Eye Effect(Chatoyance from French = Chat Oeil = Cat Eye).  This is because this quartz, due to the initial material which was replaced with silica, possesses similarly oriented fibers as inclusions.  The requirement of cutting the stone at the correct angle, which is orientation, is of prime importance to highlight the natural chatoyance.

Sri Lanka, Burma, and Germany are the best known deposits of Cat's Eye Quartz, while South Africa is home to all the rest, and also home to the vast majority of what is on the market today.  Pietersite is known from China, though not as nice in quality or color as the African stuff, and there are other smaller deposits of Tiger Eye-like material around, such as in Minnesota USA (Binghamite-Crosby, Crow Wing County), and even Arizona (Actually a chatoyant serpentine/asbestiform).  These latter types lack the brightness and availability of the African varieties.  Australia has a sub-type called Tiger Iron, but its make up is distinctly different from the various forms mentioned above.  Tiger iron is a very messy cutter, being predominantly hematite, and it is soft, and pits during polishing, except for the very highest grade. 

Except for Pietersite, Tiger's Eye and its variants are relatively inexpensive at this time, although actual Cat's Eye stones can command a premium, depending on cut, color and overall beauty.  Pietersite, being a more rare and highly polishable form, can cost upwards of $100.00 per pound for nice cutting material.




Simon and Schusters Guide To Gems

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