Realgar


Realgar, α-As<sub>4</sub>S<sub>4</sub>, 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 (As<sub>2</sub>S<sub>3</sub>). It is orange-red in colour, melts at 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur. Realgar is soft with a Mohs hardness of 1.5 to 2 and has a specific gravity of 3.5. Its molecular weight is 106.99. Its streak is orange colored. Realgar has a sub-metallic luster.