proustite
/ˈpruːstʌɪt/Mineralogy
noun
A mineral which is a sulphide of silver and arsenic and usually occurs as masses of prismatic, scarlet crystals.
- Formula: Ag3AsS3. Crystal system: trigonal..
Origin
Mid 19th century; earliest use found in Charles Shepard (1804–1886). Fromthe name of Joseph Louis Proust, French chemist, who first identified the mineral + -ite, after French proustite (F. S. Beudant Traité élém. de min. (ed. 2) II. 445).