a native red or orange arsenic(II) sulfide, As2S2 ( red orpiment, red arsenic, ruby arsenic, ruby sulfur)

Realgar, α-As4S4, is an arsenic sulfide mineral. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment (As2S3). It is orange-red in colour, melts at 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur.