Wiktionary
gratonite
n. (context mineral English) A trigonal-ditrigonal pyramidal mineral containing arsenic, lead, and sulfur.
Wikipedia
Gratonite
Gratonite is a lead-arsenic sulfosalt mineral, with the chemical composition PbAsS. Gratonite was discovered in 1939 at the Excelsior Mine, Cerro de Pasco, Peru. It is named in honor of geologist L. C. Graton (1880–1970), who had a long-standing association with the Cerro de Pasco mines.