Iodargyrite

iodargyrite

bismoclite

descloizite

bromargyrite

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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

Hydrothermal 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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