Sulfur has a structure composed of 8 sulfur atoms linked in a ring. Realgar's structure alternates between sulfur atoms and arsenic atoms producing rings of As 4 S 4 . The arsenic atoms affect the structure altering it from sulfur's orthorhombic symmetry to realgar's monoclinic symmetry. Realgar occurs in hydrothermal veins with valuable metal sulfide ores and its bright red color can be an aid to prospectors. Realgar is famous for some wonderfully beautiful specimens.
Some specimens can have a deep ruby red color with an amazing clarity and a high luster.
The color of realgar is truly something to appreciate and cherish. But realgar's beauty is sometimes fleeting. It is an unstable mineral and will alter to a different mineral, pararealgar and eventually to a powder. This process takes time and is accelerated by exposure to light. Specimens should be stored in dark, enclosed containers, and only exposed to light for the brief enjoyment of its owner and friends.