Formula: HgCl (Hg1+Cl)
Chloride of mercury, calomel group, forms a series with kuzminite
Crystal System: Tetragonal
Specific gravity: 7.15 measured, 7.23 calculated
Hardness: 1½ TO 2
Streak: Light yellowish white
Colour: Colourless, white, greyish, yellowish white, yellowish grey to ash-grey, brown; darkens upon exposure to light
Luminescence: Fluoresces brick-red under UV
Solubility: Insoluble in water, soluble in aqua regia

Hydrothermal environments

Calomel is an uncommon secondary mineral formed in the oxidised zone of mercury-bearing deposits through the alteration of other mercury minerals. Associated minerals include mercury and its amalgams, cinnabar, mercury-bearing tetrahedrite, eglestonite, terlinguaite, montroydite, kleinite, moschelite, kadyrelite, kuzminite, chursinite, kelyanite, calcite, limonite, and clay minerals (HOM, Dana, Mindat).


The type locality is Landsberg, Obermoschel, Nordpfälzer Land, Donnersberg District, Rhineland-Palatinate, Germany.

At El Doctor, Cadereyta Municipality, Queretaro, Mexico calomel occurs as an alteration of selenium-bearing metacinnabar (Dana ).

At the Funderburk prospect, Pike county, Arkansas, USA, calomel occurs in fractures in sandstone with artsmithite (Minrec 35.4.344).

At the Clear Creek claim, Goat Mountain, New Idria Mining District, San Benito county, California, USA, calomel occurs very rarely as coatings and crystals to 0.1 mm associated with native mercury, montroydite, cinnabar and, very rarely, hanawaltite (Minrec 36.4.342).

At the McDermitt Mine, Opalite Mining District, Humboldt County, Nevada, USA, calomel is associated with kleinite and terlinguacreekite in silicified volcanic rocks and sediments (CM 43.1055-1060).

At the Perry Pit, Mariposa Mine, Brewster County, Texas, USA, olive-brown light-tarnished calomel is associated with powdery aggregates of lemon-yellow terlinguacreekite in a calcitegypsum vein (CM 43.1055-1060).

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