Hawk's Eye

Hawk's eye is the blue precursor to tiger's eye. Both start as crocidolite - a blue asbestos mineral with a fibrous crystal habit. When silica-rich groundwater infiltrates crocidolite deposits, quartz gradually replaces the crocidolite fibers while preserving their fibrous structure. This pseudomorphic replacement creates a fibrous quartz aggregate that shows chatoyancy (the silky, cat's eye shimmer).

In hawk's eye, the replacement is incomplete or the original crocidolite color is preserved - the iron in the fibers remains in its original blue oxidation state (Fe²⁺). When the iron is further oxidized to Fe³⁺ (rust-like state), the color changes from blue to golden brown, producing tiger's eye. So hawk's eye represents an earlier stage in the same geological process that creates tiger's eye.

Some specimens show both blue hawk's eye and golden tiger's eye in the same piece, representing the transition zone where oxidation was partial.

Hawk's eye is identified by its blue-gray to steel-blue color combined with the characteristic silky chatoyancy (cat's eye effect) when the stone is rotated. The shimmer runs across the fibrous structure, creating a moving band of light.

Distinguish from blue tiger's eye (same material, just a name preference), sodalite (massive, no chatoyancy), and blue aventurine (sparkly rather than silky, different mineral). The chatoyant shimmer is the key diagnostic feature - no other common blue stone shows this specific silky light effect.