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Calomel Crystals from Type Locality

The Mineral calomel

Calomel is an uncommon mineral found in mercury deposits. It is one of the better-known mercury compounds, and may even be associated together with Native Mercury liquid droplets. Calomel is often found together with Cinnabar, the most common mercury compound, and may form as an alteration product of the Cinnabar.

Calomel derives its name from the Greek term "kalos", beautiful and "melos", black, in reference to its habit of turning black when coming into contact with ammonia.
Chemical Formula HgCl
Composition Mercury chloride
Color Colorless, white, light yellow, cream, gray. May darken upon prolonged exposure to light.
Streak White
Hardness 1 - 2
Crystal System Tetragonal
3D Crystal Atlas
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Crystal Forms
and Aggregates
Crystals may be tabular, prismatic, and sometimes pyramidal. Also in parallel skeletal growth, in small dense crystal groups, grainy and encrusting.
Transparency Transparent to translucent
Specific Gravity 6.4 - 6.5
Luster Adamantine
Cleavage 1,2;2,2
Fracture Conchoidal
Tenacity Sectile
Other ID Marks May be very strongly fluorescent with an orange to orange-red color.
Complex Tests Turns black upon contact with ammonia.
In Group Halides
Striking Features Color and luster, occurrence in known mercury deposits, sectility, and strong fluorescence.
Environment As a secondary mineral in mercury deposits.
Rock Type Sedimentary
Popularity (1-4) 3
Prevalence (1-3) 3
Demand (1-3) 2


Calomel is an ore of mercury.

Calomel is an uncommon mineral, found primarily in known mercury deposits. Some of the better known localities for this mineral include Landsberg, Rhineland-Palatinate, Germany; Terlingua, Brewster Co., Texas; and the Challenge deposit, Emerald Lake Hills, San Mateo Co., California.

Cinnabar, Mercury, Metacinnabar, Calcite, Terlinguaite, Eglestonite

calomel PHOTOS
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