Osarizawaite

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Formula: Pb(Al₂Cu²⁺)(SO₄)₂(OH)₆
Anhydrous sulphate containing hydroxyl, alunite group
Specific gravity: 3.89 to 4.037
Hardness: 3 to 4
Streak: Light green
Colour: Greenish yellow
Solubility: Insoluble in water and nitric acid; decomposed by boiling concentrated hydrochloric or sulphuric acid (Dana)
Environments:

Hydrothermal environments

Osarizawaite is an uncommon secondary sulphate in the oxidised zone of hydrothermal lead-zinc-copper deposits (Webmin, HOM). Associated minerals include anglesite, beaverite, hidalgoite, duftite, bindheimite, conichalcite, olivenite, quartz, clay and goethite (HOM).

Localities

At the Iodide mine, Mineral Hill Field, central New South Wales, Australia, osarizawaite has been found intimately mixed with bindheimite and mimetite. It is common in quartz-rich ore as coatings on gossan and tiny crystals associated with cerussite and pyromorphite. Rarely it occurs as epimorphs after pyromorphite. It sometimes occurs in veins in siliceous gossan, but mostly it occurs replacing pyromorphite (AJM 11.113-114).

At the Shangri La mine, Kimberely, Western Australia, Crystals of osarizawaite to 40 microns form thin crusts on the surfaces of cavities and boxworks in quartz veins, sometimes associated with anglesite (AJM 16.1.22).

At Whim Creek, Roebourne Shire, Western Australia, there is a copper-zinc-lead sulphide deposit that outcrops as a gossan consisting largely of secondary hematite, goethite and quartz, and with locally abundant malachite. Other secondary minerals,including osarizawaite, occur erratically, and mostly in microscopic amounts. The osarizawaite has so far been found in only one gossan sample from Whim Creek, where it occurs as microscopic spots consisting largely of tiny hexagonal rings. Minerals of the alunite-jarosite group exhibit wide compositional ranges due to substitutions in both cation and anion positions; it is plausible that, during supergene alteration, crystals grew with concentric zones of different composition, and when the supergene solutions changed so as to make one or more of the zones unstable, the unstable zones were dissolved away, leaving the relatively insoluble rims to be retained as rings (AM 65.1287-1290).

At the type locality, the Osarizawa mine, Kazuno City, Akita, Japan, osarizawaite occurs in the oxidised zone as a powdery crust on anglesite and limonite. Other minerals present in the oxidised zone are linarite, azurite, brochantite, malachite and kaolinite (AM 47.1216-1217).

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