Calomel
Image: Darla Sondrol (CC0)
Mineral NameCalomel
Chemical FormulaHgCl
Mohs Hardness1
Crystal Systemtetragonal
Lusteradamantine
Streak Colorpale yellowish white
Cleavagegood on {110}
Fractureconchoidal to uneven
Specific Gravity7.15
Colorswhite, yellowish, grayish, brownish
Transparencytransparent to translucent
Type LocalityAlmadén, Spain; Idrija, Slovenia; Terlingua, Texas, USA
Mineral GroupHalides
Usescollector, historical medicine, pigment
Associated Mineralsnative mercury, cinnabar
Rarityuncommon
Description
Calomel in this sample appears as a yellow, earthy coating or small crystalline aggregates, contrasting with the reddish cinnabar and liquid mercury.
Geological Context
Calomel is a secondary halide mineral that forms in the oxidized zones of mercury ore deposits, typically as an alteration product of primary mercury minerals like cinnabar or native mercury, often in arid environments.
