Orpiment Composition, Crystallization, Structure and Occurrence

Composition. Arsenic trisulphide, As2S3 = Sulfur 39, arsenic 61.

Crystallization. Monoclinic. Crystals small and rarely distinct. 

Structure. Usually foliated.

Physical Properties. Very perfect cleavage parallel to clinopinacoid. Folia flexible but not elastic. Sectile. H. = 1.5-2. G. = 3.4-3.5 . Resinous luster, pearly on cleavage face. Color lemon-yellow. Translucent..

Test. Same as for realgar (Which see). Characterized by its yellow color, perfect cleavage and foliated structure.

Occurrence. A rare mineral, associated usually with realgar and formed under similar conditions. Found in various places in Rumania; in Kurdistan; in Peru, Japan, etc. Occurs at Mercur, Utah and at Manhattan, Nevada. Deposited form geyser waters in the Yellowstone Park.

Name. Derived form the Latin, auripigmentum, “Golden paint”.

Use. For a pigment, in dyeing and in a preparation for the removal of hari from skins. Artificial arsenic sulfide is largely used in place of the mineral.