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Formula: KFe3+3(SO4)2(OH)6
Anhydrous sulphate containing hydroxyl, the most common member of the
alunite group
Crystal System: Trigonal
Specific gravity: 2.9 to 3.26 measured, 3.25 calculated
Hardness: 3 to 4
Streak: Yellow
Colour: Ochre-yellow, brown to blackish brown
Solubility: Insoluble in water, moderately soluble in hydrochloric acid
Common impurities: Na,Ag,Pb
Environments:
Hydrothermal environments
Hot springs
Jarosite is a secondary sulphate found in the oxidation
zone of
hypothermal (high temperature) veins and sulphide deposits, particularly
pyrite-bearing
deposits, formed by weathering in arid climates
(Webmin, MW).
It is formed by the reaction of sulphuric acid derived from the oxidation of
pyrite,
and
is usually accompanied by limonite
(Dana).
Less commonly it occurs as a low-temperature, primary
hydrothermal mineral, including in deposits around hot springs. Associated minerals include
alunite and
pyrite
(HOM).
Localities
At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the
copper
ores overlie primary zone mineralisation consisting of
quartz-dolomite-sulphide veins hosted
in siltstone and schist.
Jarosite occurs as partial pseudomorphs after fibrous
goethite, associated with hematite
and pyrite
(AJM 22.1.24).
In the Mount Isa region of northwest Queensland, Australia, minerals of the
alunite-jarosite family occur in
gossan
related to lead-zinc mineralisation
associated with dolomitic
shale. The mineralogy of
gossan and
ironstone from these
shale- or
slate- hosted deposits is almost invariably
goethite, hematite,
quartz, minerals of the
alunite-jarosite
family, muscovite and kaolinite
(AM 72.178-187).
At the Almanda mine, Cherry Gardens, South Australia, microcrystals of jarosite to 10 microns have been found
on weathered
phyllite
(AJM.18.1.56)
At Tom's quarry, Kapunda, South Australia, jarosite lines cavities in
apatite- and
quartz-rich rocks
(AJM 17.1.29).
At Moculta, South Australia, jarosite occurs in apatite-rich rocks as
0.5 mm crystals associated with highly corroded pyrite
(AJM 17.1.29).
At At Mount Moliagul, Moliagul, Central Goldfields Shire, Victoria, Australia, minute crystals or coatings of
jarosite,
often associated with natrojarosite, occur in cavities in
quartz
(AJM 21.1.43).
At the Mount Deverell variscite deposit, Milgun Station, Western Australia,
jarosite
is widespread coating surfaces and in veins in siltstone. The
variscite deposits are hosted by
marine sedimentary rocks
(AJM 20.2.26).
At the Northampton field, Western Australia, jarosite and natrojarosite have been reported in shear zones
alongside or
within pegmatite veins, formed as the result of the weathering of pyrite and
marcasite in acid gneiss
(AJM.18.1.44).
At Moxom's Well, Braeside lead field, Pilbara, Western Australia, jarosite has been found as earthy coatings
on altered
pyrite
(AJM 13-2.60).
At Llallagua, Bolivia, massive jarosite has been found with limonite
in the
centres of larger veins, and it occurs very rarely as small crystals
(Minrec 37.2.140).
In Alpine-type fissures and the talc deposit at Saint-Pierre-de-Broughton, Quebec,
Canada, jarosite is found as an alteration
product of pyrite in weathered rocks, associated with
limonite pseudomorphs after
pyrite
(R&M 85.6.504).
The type locality is the Jaroso Ravine, Sierra Almagrera, Cuevas del Almanzora, Almería, Andalusia, Spain.
Jarosite from the Jaroso Ravine - Image
At the Alderley Edge, Mottram St Andrew area, Cheshire, England, UK, microcrystalline to powdery jarosite was
found
in conglomerate associated with galena
(JRS 5.2.98).
At Brownley Hill, Alston Moor, Cumbria, England, UK, earthy jarosite is common in the
shale beds both above and below the Great Limestone, apparently formed by
the post-mining oxidation of pyrite
(Minrec31.3.246)
At the Newhurst quarry, Shepshed, Leicestershire, England, UK, jarosite has been found as microcrystalline
crusts and masses often associated with azurite and
malachite, or as a coating on them
(JRS 8(2).56).
At Gwaith-Yr-Afon mine, Dyfed, Wales, UK, a mineral forming thin drusy crusts on heavily corroded
chalcopyrite has been tentatively identified as jarosite. It is
occasionally overgrown by later langite and
brochantite
(JRS 5(2).111).
At the Cae Coch Mine, Trefriw, Gwynedd, Wales, UK, jarosite occurs with
fibroferrite and copiapite
(MW).
At the Dolyhir Quarry, Old Radnor, Powys, Wales, UK, jarosite has been found forming microcrystalline crusts in
fractures associated with brochantite
(MW).
At Penarth and Lavernock, South Wales, UK, crusts of jarosite occur on
shale
exposed in sea cliffs a short distance south of Penarth
(MW).
At the Gallagher vanadium property and Manila mine, Cochise county, Arizona, USA, jarosite is common,
particularly at the Manila site where crystals to 5 mm can be found associated with
native gold, bromian
chlorargyrite,
chlorargyrite,
goethite, vanadinite,
descloizite and wulfenite
(R&M 90-4.343).
Jarosite from the Gallagher vanadium property -
Image
At the Brown Monster mine, Inyo county, California, USA, jarosite, sometimes with
mottramite, is occasionally found with
mimetite
on fracture surfaces in limestone
(Minrec 41.2.188).
At the Cripple Creek mining district, Colorado, USA, jarosite occurs as crystals filling small
quartz druses, and as pseudomorphs
after pyrite
crystals in oxidised breccia, sometimes associated with
baryte
(Minrec 36.2.173).
At the Apex mine, Lander County, Nevada, USA, microcrystalline drusy crusts and single crystals of jarosite
rarely as associates of torbernite and
autunite
(R&M 87-3.274-275).
Jarosite from the Apex Mine - Image
At the Tintic Mining District, Juab County, Utah, USA, jarosite is quite common and is present in most of the
mines, especially when there is pyrite that has begun to oxidise. The
jarosite forms a bright brownish yellow, extremely fine powder consisting of minute yellow hexagonal scales.
In the Colorado #1 mine large walls and boulders completely covered in brown crystals of jarosite once were
found in a small tunnel that has since been sealed; on many of the specimens from this find,
pseudomorphs and casts of jarosite after other minerals can be
observed.
(MinRec 55.2.206-207).
Jarosite from Tintic - Image
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