Sillimanite Cat's Eye

is sometimes referred to as “fibrolite” because its crystals occur in groups, resembling fibers. It is found throughout the world, in Myanmar (Burma), Sri Lanka (Ceylon), the U.S. (Idaho), Czechoslovakia, India, Italy, Germany, and Brazil.
Sillimanite (also known as Fibrolite) is found in various colours including green, yellow, brown, blue, white and even black. The gem is a complete Jekyll and Hyde; it can be discovered as a truly transparent gem, or completely opaque with a waxy lustre.
Sillimanite from a variety of high-grade metamorphic rocks contains from 0-13 to 1-82 weight per cent Fe2O3 and less than 0-1 weight per cent TiO2. The iron is trivalent and substitutes for Al only.
In technical terms the cats eye effect is called Asterism. There are many gemstones that can show this effect including Chrysoberyl, Quartz, Apatite and Tourmaline. I ti caused by tiny inclusions within the stone that concentrate light along the center of the stone when it is cut into a cabochon.