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Formula: Tl(Mn4+7.5Cu2+0.5)O16
Oxide, coronadite group
Crystal System: Tetragonal
Specific gravity: 5.285 calculated
Environments
Sedimentary environments
Hydrothermal environments
Thalliomelane is a relatively new mineral, approved in 2019 and to date (June 2022) reported only from the type
locality.
Localities
At the type locality, the Zalas quarry, Gmina Krzeszowice, Kraków County, Lesser Poland Voivodeship, Poland,
thalliomelane was discovered in relics of supergene
mineralisation disseminated in a fault breccia in sandy
limestone. It occurs rarely and exclusively in the form of fibrous
and highly porous tiny aggregates <50 µm in size that fill small fractures and voids in the sandy
limestone host rock.
The formation of thalliomelane was most probably connected to the weathering of a sulphide mineral assemblage
under semi-arid to arid conditions. It resulted in the release of thallium
and other components of the mineralisation into water under the influence of chlorine-, bromium- and iodine-bearing
brines or from sediments. Due to the interaction of these waters, the
primary ores altered, mainly into
goethite, cuprite,
malachite and manganese oxides of the
coronadite type, with subordinate copper sulphates, lead arsenates,
bismuth oxy-chlorides and traces of
iodargyrite.
This assemblage indicates oxidation at a progressively increasing pH (alkalinity) of around 8 to 10, where
thalliomelane could have formed from a cryptomelane-type manganese
oxide in contact with thallium-bearing aqueous solutions
(AM 106.2020-2027).
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