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Formula: AgI
Normal halide
Crystal System: Hexagonal
Specific gravity: 5.69 measured, 5.709 calculated
Hardness: 1½ to 2
Streak: Yellow (shining)
Colour: Colourless (fresh); pale yellow, yellow, greenish yellow, brownish, greyish
Common impurities: Cl,Br
Environments
Iodargyrite is a secondary mineral associated with weathered
silver ores
(Webmin, HOM) in arid regions
(Dana).
Associated minerals include bismoclite, silver,
acanthite, chlorargyrite,
bromargyrite, calcite,
cerussite, descloizite,
pyromorphite, vanadinite and
limonite
(HOM, Mindat).
Localities
At the Mount Deverell variscite deposit, Milgun Station, Western Australia, iodargyrite
occurs as microscopic grains included in
rutile/anatase,
and in cavities in jarosite replacing
pyrite. It has
also been found in an alunite
pseudomorph
after pyrite in
variscite. The variscite
deposits are hosted by
marine sedimentary rocks
(AJM 20.2.26).
The Chibougamau mining district, Nord-du-Québec, Québec, Canada.
Iodargyrite, together with associated minerals chlorargyrite,
bromargyrite and bromian
chlorargyrite,
form a group of secondary minerals that in terrigenous
(made of material eroded from the land)
supergene environmens worldwide, are exclusively confined to
oxidised
sulphide zones formed in arid and semi-amid climates. The presence of iodargyrite in
gold-bearing glacial sediments of the Chibougamau-Chapais area of Quebec,
together with
other indicators of an arid climate, provides cogent evidence of a past arid climate in this region. These indicators
include:
a) the existence of a deep water table during sulphide ore oxidation of Chibougamau copper
deposits,
b) the abundance of 'limonite dice' in glacial tills, indicative of the
pseudomorphic replacement of pyrite grains
in bedrock formations under arid conditions,
c) the abundance of spongy and corroded grains of gold typical of
lateritic terranes, and
d) the abundance of possibly desert-derived quartzofeldspathic sand formations.
A period of aridity in the Tertiary is suggested
(CM 35.23-34).
At Dzezkazgan, Kazakstan, iodargyrite has been found with malachite
(FM 42699).
The type locality is the Albarradón Mine, Concepción del Oro Municipality, Zacatecas, Mexico.
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