Traditionally, in pre-scientific times all cat’s eyes were supposed to come from chrysoberyl but the last decades have taught the gem buying public that cat’s eyes are found in many varieties, in fact most gemstones produce cat’s eye effects sometimes, more or less attractive, tourmaline, aquamarine, garnets, etc. in all shades and hues.
Yet, many gem dealers for astrology and healers in India, Malaysia or Indonesia ignore this fact and sell any brown or green cat's eyes as chrysoberyls and make a killing by ‘upgrading’ apatite or silimanite cat’s eyes to the real deal. And, who knows, perhaps these do the job as well as the expensive chrysoberyl do. They are, after all, also natural cat’s eyes, not fakes and also untreated. So, just perhaps, no harm is done.
The optical source for a cat’s eye is in principle the same as what we find in stars. The latter shows 3 rays crossing ideally in the top center with 60 degrees to one another and produce a six-rayed star. Twelve rays, produced by six cat’s eyes are also found, as are star’s with only four rays or two cat’s eyes.
While the back of a cat’s eye remains unpolished it should be small, flat, symmetric, and ideally conic to help the goldsmith with a setting.
What is important in a cat’s eye? The ray is. The stronger and sharper the ray the better, plus it should be centered, focused, mobile, easily visibile, symmetrical and straight, not crooked.
The connoisseur also values the ray’s own color, ranging from yellow to bluish, milky white, silvery or platinum.
Secondly, comes the body of the gem, the more translucent the body, the better; its color should be pleasant but will always dimmed by the needle structure (as any silky inclusion or diesel would in a facetted gem).
Ideally, in chrysoberyl and in apatite, but not in all varieties, the ray shall part the gem in two color spheres when 'torched' from the side, one brighter half and one darker or even two completely different hues. In a gem collector’s life, there is no end to discovering novelties. Promise.