Class : Halides
    Subclass : Oxychlorides
    Crystal system : Monoclinic
    Chemistry : Hg₂ClO
    Rarity : Very rare

Terlinguaite is a rare oxychloride found in the oxidation zone of mercury deposits, particularly in desert regions. It results from the alteration of cinnabar in an environment rich in chlorides, which can be brought by outcropping evaporites or by saline air if the deposit is close to the sea. In addition to cinnabar, it is almost always accompanied by calomel and eglestonite, two other mercury chlorides, and native mercury. Its name comes from its discovery location : Terlingua (Texas). Terlinguaite occurs in powdery masses or in multiform crystals, frequently isometric, elongated along [010] or flattened on {001}. The mineral is of variable hue, generally orange-brown, yellowish to greenish, turning brown on exposure to light with a strong adamantine luster. Of low hardness (2.5), it is also very dense (more than 8.7).

Main photo : Terlinguaite from Mariquita Mine, Spain © Borja Sainz de Baranda Graf

No twinning known for this mineral species.

No fakes listed for this mineral species.