Realgar ( ree-AL-gar, -⁠gər), also known as "ruby sulphur" or "ruby of arsenic", is an arsenic sulfide mineral with the chemical formula α-As₄S₄. 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 color, 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 streak is orange colored. It is trimorphous with pararealgar and bonazziite. Its name comes from the Arabic rahj al-ġār (رهج الغار, "powder of the mine"), via Medieval Latin, and its earliest record in English is in the 1390s.