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Calomel, Terlinguaite-222734.jpg
Terlinguaite, collected from Mariposa Mine, Terlingua District, Brewster County, Texas, United States
Category Halide mineral
(repeating unit)
Strunz classification 3.DD.20
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/c
Unit cell a = 19.51 Å, b = 5.91 Å
c = 9.47 Å; β = 143.81°; Z = 4
Color Sulfur-yellow, greenish yellow, brown
Crystal habit Aggregates of equant to elongated crystals, powdery, massive
Cleavage Perfect on [101]
Tenacity Brittle
Mohs scale hardness 2.5
Luster Brilliant adamantine
Streak Lemon-yellow, turning olive-green
Diaphaneity Transparent to translucent
Specific gravity 9.22
Optical properties Biaxial (-)
Refractive index nα = 2.350 nβ = 2.640 nγ = 2.660
Birefringence δ = 0.310
Pleochroism Weak, green and yellow
2V angle Measured: 20°
Alters to turns olive-green on exposure to light
References [1][2][3]

Terlinguaite is the naturally occurring mineral with formula Hg2ClO. It is formed by the weathering of other mercury-containing minerals. Discovered in 1900 in the Terlingua District of Brewster County, Texas for which it is named.[4] Its color is yellow, greenish yellow, brown or olive green.


  1. ^ Handbook of Mineralogy
  2. ^ Mindat.org
  3. ^ Webmineral data
  4. ^ Hillebrand, W. F.; W. T. Schaller (1907). "Art. XXVI. "The Mercury Minerals from Terlingua, Texas: Kleinite, Terlinguaite, Eglestonite, Montroydite, Calomel, Mercury"". The American Journal of Science (139): 259–274. Retrieved 2009-05-21.