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Formula: Pb2+4(S2O3)O2(OH)2
One of a relatively small group of thiosulphate minerals (a thiosulphate is a salt containing the anion
[S2O3]2−, i.e. a sulphate with one oxygen atom replaced by sulphur) .
Crystal System: Triclinic
Specific gravity: 6.765 calculated
Hardness: 1 to 2
Streak: Cream-coloured, off-white, white
Colour: Colourless, beige
Luminescence: Not fluorescent under UV
Solubility: In dilute hydrochloric acid, there is only an initial effervescence, after which the material turns to
a chalky white colour within a few minutes (Mindat)
Environments
Localities
At the type locality, the Tsumeb Mine, Tsumeb, Oshikoto Region, Namibia, sidpietersite was identified on a
single sample that has been split for scientific study. The matrix of the original piece consists of a mixture of
fine-grained galena and
sphalerite. Perched on the matrix are pale pink to colourless crystals
of smithsonite, 7 to 8 mm in size, that have been partly coated by an
opaque tan-coloured crust of zincite. Minor
greenockite and quartz also
are present on and in the matrix. Sidpietersite is considered to be
secondary after galena;
masses have been observed both on the
galena-sphalerite matrix and on
the zincite-coated crystals of
smithsonite, and it is obviously the last mineral to form in this
environment.
It is postulated that thiosulphate formation occurred during an intermediate stage of oxidation as the assemblage
moved toward complete oxidation and subsequent formation of sulphate after initial deposition of the sulphide.
Sidpietersite is the first confirmed thiosulfate-bearing mineral known to occur at the Tsumeb deposit
(CM 37.1269-1273).
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