Wiktionary
arsenoclasite
n. (context mineral English) A mineral containing arsenic, hydrogen, manganese, and oxygen.
Wikipedia
Arsenoclasite
Arsenoclasite (originally arsenoklasite) is a red or dark orange brown mineral with formula Mn(AsO)(OH). The name comes from the Greek words αρσενικόν (for arsenic) and κλάσις (for cleavage), as arsenoclasite contains arsenic and has perfect cleavage. The mineral was discovered in 1931 in Långban, Sweden.