Tiger's Eye

Tiger's eye is a fibrous variety of quartz, the silicon dioxide form (SiO₂), whose silky chatoyant banding records the replacement of an earlier fibrous mineral. Tiger's eye has one of the most fascinating formation stories in mineralogy. It begins as crocidolite - a blue fibrous mineral in the asbestos family. Over millions of years, silica-rich fluids dissolve the crocidolite fibers and replace them, atom by atom, with quartz. This process (pseudomorphism) preserves the original fibrous structure while completely changing the chemistry.

The parallel arrangement of the original crocidolite fibers is what creates chatoyancy - the silky, shifting band of light that moves across the surface like a cat's eye. Iron oxide staining during or after the replacement process turns the fibers golden-brown, creating the classic tiger's eye color.

Hawk's eye (blue tiger's eye) represents an intermediate stage where the crocidolite hasn't been fully stained by iron oxide, preserving more of the original blue color. Red tiger's eye is created by gentle heating, which further oxidizes the iron. The entire transformation from blue asbestos to golden quartz pseudomorph takes millions of years.

Tiger's eye is unmistakable when you see the chatoyancy, a silky, luminous band that moves across the surface as you tilt the stone. The golden-brown color combined with this optical effect is diagnostic. At Mohs 7, it's hard and durable.

Distinguish from hawk's eye (blue-gray, same mineral but less iron staining), cat's eye chrysoberyl (much more valuable, different mineral), and pietersite (a brecciated, swirled version of tiger's eye). Under magnification, the parallel fibrous structure is visible. Tiger's eye has no cleavage and fractures irregularly.