It is an aluminate of beryllium - a mixture of aluminum and beryllium - having traces of oxide of iron and chromium, which serve as coloring agents and give it brownish and greenish tinges. It has a chatoyant glowing from inside like the eye of a cat and having white fibers. The brighter the fiber, the higher is the quality of the gem. Cat's-eye has a silky streak of light that moves with the turning of the stone like a gleam in a straight line across the stone.                                        

 

Quantities :Smoothness

Having three streaks of light, similar to the sacred thread worn by Brahmins in India Straightness of the chatoyance

Quality of mineral

High specific gravity - heavier than average stone of the same size

Brilliance of chatoyance

Cat's eye is found in many colors: yellow, black, dark or smoky-green, and white. The only thing common to all shades is the band of light moving across the stone, the chatoyance.