Pietersite (blue)

Pietersite is a natural brecciated rock (a gem material, not a single mineral species) made of fine-grained quartz or chalcedony with embedded fibres of crocidolite, an amphibole, in various stages of alteration to iron oxides. The fibres give it a chaotic, multi-directional chatoyancy in blue-gray, golden yellow, brown and red. It is often described as a brecciated tiger's eye or hawk's eye; mineral databases classify it as a variety of chalcedony. It is also called Tempest stone.