Dimorphite, chemical name
tetraarsenic trisulfide (As
4S
3), is a very rare orange-yellow arsenic sulfide mineral. In nature, dimorphite forms primarily by
deposition in volcanic
fumaroles at temperatures of 70–80 °C (158–176 °F). Dimorphite was first discovered in a such a fumarole near Naples, Italy in 1849 by the mineralologist Arcangelo Scacchi (1810–1893). Since its discovery, dimorphite has been found in the Alacrán silver mine near
Copiapó,
Chile. It has also been reported from
Cerro de Pasco,
Peru, and the Lavrion District Mines in
Attica,
Greece.