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Formula: Hg1+6Hg2+O3Cl2
Oxyhalide of mercury
Specific gravity: 9.51 calculated
Hardness: 4
Streak: Dark reddish black
Colour: Black to very dark brown-black
Luminescence: Not fluorescent under UV
Environments
Metamorphic environments
Hydrothermal environments
Hanawaltite is a very rare mineral; although it was approved in 1994, to date (September 2022) it has been
reported only from the type locality. It decrepitates on exposure to sunlight, photoreducing to
mercury
(Mindat).
Localities
At the type locality, the Clear Creek claim, Goat Mountain, New Idria Mining District, San Benito county,
California, USA, hanawaltite occurs sparingly with calomel, native
mercury, cinnabar,
montroydite and quartz in a
single specimen of float near a prospect pit. The specimen contains subhedral to anhedral black to dark brown-black
crystals of hanawaltite, typically bladed to platy, maximum size 0.3 x 0.3 mm. It is an alteration product of
cinnabar, in the mercury deposit
in brecciated silicate-carbonate rock hydrothermally altered from
serpentinite and composed mainly of ferroan
magnesite and quartz
(AM 81.1282, Webmin)
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