Cerargyrite

Ce‐rar″gy‐rite (sē̍‐rär″jy̆‐rīt), n. [Gr. κέρασ horn + ἄργυροσ silver.] (Min.) Native silver chloride, a mineral of a white to pale yellow or gray color, darkening on exposure to the light. It may be cut by a knife, like lead or horn (hence called horn silver).