Jarosite

minerals

variscite

alunite

marcasite

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Formula: KFe3+3(SO4)2(OH)6
Anhydrous sulphate containing hydroxyl, the most common member of the alunite group
Specific gravity: 2.9 to 3.3
Hardness: 3 to 4
Streak: Yellow
Colour: Ochre-yellow, brown to blackish brown
Solubility: Insoluble in water, moderately soluble in hydrochloric acid
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

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

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).

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).

Common impurities: Na,Ag,Pb

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