realgar Minor sulphide ore for arsenic, As₂S₂, associated with orpiment (As₂S₃) to which realgar changes on exposure; sp. gr. 3.6; hardness 1.5–2.0 (can be cut with a knife); monoclinic; red, varying to orange and yellow, transparent to translucent; orange-red streak; resinous lustre; crystals rare, short, striated, and prismatic, also occurs granular, compact, or massive; cleavage good pinacoidal; also found at hot springs and in limestones and dolomites; alters to yellow powder.

realgar native disulphide of arsenic. XIV. — medL. — Arab. rahj al-ġār ‘powder of the cave or mine’ (rahj powder, al AL-2, ġār cave).