Ganoine

Ganoine or ganoin is a glassy, often multi-layered mineralized tissue that covers the scales, cranial bones and fin rays in some basal ray-finned fishes. It is composed of rod-like, pseudoprismatic apatite crystallites, with less than 5% of organic matter. Existing fish groups featuring ganoin are bichirs and gars, but ganoin is also characteristic of several extinct taxa. It is a characteristic component of ganoid scales.