This mineral is distinguished by its red color, resinous luster, orange-red streak, and its association with orpiment. On long exposure to light, it disintegrates to a reddish-yellow powder. It is found in veins of lead, silver and gold ores, and as a deposit from hot springs. It is used as a pigment. The name is derived from the Arabic Rahj al ghar meaning "powder of the mine."

Mineral Photos courtesy of R.Weller/Cochise College