Calomel , Terlinguaite Locality: Perry Pit, (Ca) Mariposa Mine, Terlingua District, Brewster County, Tx, USA Original description: Amber calomel crystals and bright yellow terlinguaite on gossan matrix, 3 mm. across. Collected c. 1995 R Stegemoller. The calomel crystal's transparent and appears to contain some cinnabar inclusions. — Photo: Kelly Nash · CC BY 3.0
Terlinguaite
A yellow mercury oxychloride formed by weathering of mercury ores at Texas's Terlingua district.
Intro adapted from Wikipedia (CC BY-SA).
Terlinguaite is an IMA-recognized mineral species in the halide class, with the chemical formula Hg₂OCl.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 2.5; specific gravity 9.22; Lemon-yellow, turning olive-green streak; Brilliant adamantine luster; optically biaxial.
IMA symbol Tlg, grandfathered status — known before the IMA’s founding, named in 1900.
Found as a rare secondary mineral in hydrothermal mercury deposits.
It is found associated with Cinnabar, metacinnabar, eglestonite, kleinite, montroydite, calomel, mercury.
The name refers to its occurrence at Terlingua, Texas, USA.