Calomel

Calomel is a mercury chloride mineral with formula Hg2Cl2 (see mercury(I) chloride). The name derives from Greek kalos (beautiful) and melas (black) because it turns black on reaction with ammonia. This was known to alchemists.Calomel occurs as a secondary mineral which forms as an alteration product in mercury deposits. It occurs with native mercury, amalgam, cinnabar, mercurian tetrahedrite, eglestonite, terlinguaite, montroydite, kleinite, moschelite, kadyrelite, kuzminite, chursinite, kelyanite, calcite, limonite and various clay minerals.The type locality is Moschellandsburg, Alsenz-Obermoschel, Rhineland-Palatinate, Germany.