Realgar
a monoclinic mineral, occurring but rarely in crystals, but mostly granular to compact-massive. Hardness, 1.5-2; sp. gr., 3.4-3.6; luster, resinous; color and streak, aurora-red to orangeyellow; transparent to translucent; fracture, conchoidal; brittle. Occurs in fine crystals in Hungary and Transylvania, formed artificially by heating arsenic acid with the proper proportion of sulphur. It is a fusible and volatile substance, having an orange-red color, is used for painting and for the production of white-fire.