pearceite
/ˈpɪəsʌɪt/Mineralogy
noun
A black, lustrous, brittle mineral consisting of a sulphide of silver and arsenic, Ag16As8S11, occurring as tabular crystals of the monoclinic system and usually containing copper in place of some of the silver.
Origin
Late 19th century. From the name of Richard Pearce, British-born metallurgist and chemist + -ite.