Osakaite

osakaite

hydrozincite

smithsonite

chlorite

Images

Formula: Zn4(SO4)(OH)6.5H2O
Hydrated sulphate of zinc, namuwite group
Crystal System: Triclinic
Specific gravity: 2.70 measured, 2.75 calculated for the empirical formula
Hardness: 1
Streak: White to pale blue
Colour: Pale blue to colourless or white
Luminescence: No fluorescence under UV
Solubility: Easily soluble in dilute hydrochloric and nitric acids
Environments

Hydrothermal environments

Partial dehydration of osakaite may result in lahnsteinite (Mingen).

Localities

The type locality, the Hirao mine, Onsen-cho, Minoh City, Osaka Prefecture, Japan, is developed in shale. The primary ore-minerals are sphalerite, chalcopyrite, pyrite and galena. Among them, sphalerite is predominant, and the mineral is disseminated through the host rock, which consists of chlorite altered during a hydrothermal alteration process. In the mine, many secondary minerals such as smithsonite, hydrozincite, schulenbergite, the zinc-dominant analogue of schulenbergite, brianyoungite, hemimorphite, brochantite, ramsbeckite, aurichalcite, malachite, azurite, posnjakite and ktenasite occur on the gallery wall and in cracks in the altered shale.
Osakaite is one of the secondary minerals; it occurs in two different aspects. The first type occurs as hexagonal platy crystals up to 0.5 mm across and 0.01 mm in thickness in the form of stalactitic aggregates up to 2 cm long. The second type occurs in cracks in the altered shale. The associated minerals are hydrozincite, smithsonite, chlorite and limonite.
It is likely the osakaite was formed in zinc-, copper- and SO4- bearing groundwater derived from sphalerite and chalcopyrite in the host rock at around 20°C (CM 45.6.1511-1517).
Osakaite from the Hirao Mine - Image

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