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.

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