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Formula: Pb2+5(OH)5[Cu1+(S6+O3S2-)3](H2O)2
Anhydrous thiosulphate (containing [S2O3]2- groups)
Crystal System: Monoclinic
Specific gravity: 5.150 calculated
Streak: White
Colour: Colourless, white
Luminescence: Not fluorescent under UV
Environments
Steverustite is a relatively new mineral, approved in 2008
Localities
At the type locality, the Frongoch Mine, Pontrhydygroes, Upper Llanfihangell-y-Creuddyn, Ceredigion, Wales, UK,
supergene steverustite, a thiosulphate of
lead and copper, was first described
from the waste dumps. It occurs as minute lathlike crystals to 0.75 mm, fibrous or acicular in habit, typically
aggregated to form fibrous bundles. It occurs in quartz veinstone in small
cavities, up to a few millimeters across, associated with galena,
sphalerite, and a range of
supergene minerals including
anglesite, bechererite,
caledonite, cerussite,
hemimorphite and susannite.
Steverustite is late in the paragenesis, forming after caledonite
and bechererite from the late-stage oxidation of
galena.
Thiosulphate minerals (salts of the (S2O3)2- ion) are extremely rare; at the time of
this writing (R&M June 2021) steverustite is one of
only four IMA-approved species containing the thiosulphate group, others being
bazhenovite, redmondite and
sidpietersite. Nevertheless, steverustite has now been reported
from no less than seventeen localities worldwide, nine of which are in Wales (www.mindat.org; accessed June 2021).
(R&M 97.4.380-381).
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