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Formula: (Hg2N)Cl
Chloride
Crystal System: Isometric
Specific gravity: 7.72 measured, 7.53 calculated
Hardness: 3 to 4
Streak: Very light yellow
Colour: Yellow, turns olive-green upon prolonged exposure to light
Solubility: Alters to a white substance retaining its original shape when placed into cold hydrochloric acid
Environments
Mosesite is a rare secondary mineral formed at low temperature
in hydrothermal mercury deposits. Associated minerals include
calcite, cinnabar,
metacinnabar, mercury,
eglestonite, kleinite,
terlinguaite, montroydite,
calomel and gypsum
(HOM).
Localities
At the San Luis Mine, Huahuaxtla, Mun. de Taxco, Guerrero, Mexico, mosesite occurs with
terlinguaite, montroydite,
eglestonite and calomel
(Dana).
At the Mariquita Mine (Sultana Mine), Usagre, Badajoz, Extremadura, Spain, mosesite has been found as
microcrystalline aggregates and masses of a very vivid lemon-yellowish colour, associated with
cinnabar, baryte and
calcite. Mosesite also has been found associated with globular
masses of montroydite formed by oxidation of
native mercury droplets
(MinRec 55.4.505).
Mosesite from the Mariquita Mine -
Image
At the type locality, the Terlingua Mining District, Texas, USA, mosesite occurs as small, isolated, yellow crystals
on calcite, associated with montroydite
and gypsum
(AJS 30.202-208, Mindat).
Mosesite from Terlingua - Image
At Clack Mine, Willard Mining District, Humboldt Range, Pershing County, Nevada, USA, the chief ore mineral in the
mercury deposit is cinnabar; the country
rock is a fine-grained, massive, medium-grey limestone, and the
cinnabar together with crystalline calcite
occurs as a replacement in veins and in small irregular masses
(AM 17.541-550).
Genesis
Mosesite may be easily synthesised by treating HgCl with dilute ammonium hydroxide according to the reaction:
4NH4OH + 4HgCl → 2Hg + Hg2NCl.H2O +3H2O +3NH4Cl.
In terms of minerals this would be equivalent to the reaction of ammonia-bearing waters with
calomel, yielding native mercury and
mosesite. As calomel, mosesite, and native
mercury are all found at Terlingua and Huahuaxtla, it is quite probable that the
mosesite was formed in just this way, probably at very low temperature because the synthesis may be done at
25oC.
At the Huahuaxtla mine, the ammonia may have come from the highly carbonaceous
shale lying immediately above the Pozcr Rico cave
(AM 38: 1225-1234.).
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