Namuwite

Formula: Zn₄(SO₄)(OH)₆.4H₂O
Hydrated sulphate, namuwite group
Crystal System: Trigonal
Specific gravity: 2.77 measured, 2.81 calculated
Hardness: 2
Streak: Pale green
Colour: Sea green
Common impurities: Cu

Hydrothermal environments

Namuwite is a very rare secondary mineral; it is a post-mining phase, typically formed through the oxidation of sphalerite-bearing veinstone in mine workings and within zinc and copper rich mine dumps (MW). Associated minerals include hydrozincite, schulenbergite, serpierite, ktenasite, devilline and gypsum (HOM).

Localities

At the Smallcleugh Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, pearly sea-green namuwite forms flat, triangular plates up to 200 microns across. Only rarely do the crystals show development of the full hexagonal plates seen on the type specimen. The plates are commonly curved, and are typically grouped together as sheaves. Serpierite is present as turquoise to copper-blue mm-long bundles comprising wispy or stellate acicular groups. Textural evidence tentatively suggests that schulenbergite and namuwite at Smallcleugh Mine formed later than the serpierite and as the former have lower copper:zinc ratios than serpierite it appears that within the supergene assemblage copper became progressively depleted (JRS 3.23-24).

At the Frongoch Mine, Devil's Bridge, Ceredigion, Wales, UK, namuwite occurs very rarely as crystal clusters to 0.5 mm on quartz-galena veinstone. It is clearly post-mining in origin and late in the paragenesis, typically overgrowing langite, wroewolfeite, susannite or hydrocerussite (MW).

At the type locality, the Aberllyn mine, Betws-y-coed, Gwydyr Forest area, Conwy, Wales, UK, namuwite occurs encrusting hydrozincite (Dana) on a breccia composed of slate fragments cemented by sphalerite, quartz, calcite and ankerite (AM 81.238-243, Mindat, MW).

At the Dylife Mine, Penegoes, Powys, Wales, UK, namuwite is associated with schulenbergite on altered sphalerite (MW).

At Balmat, St Lawrence county, New York, USA, namuwite is associated with magnetite (Minrec 41.6.536).

Back to Minerals