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Formula: Pb3Cl4(Se4+O3).H2O
Valence: Pb2+3Cl4(Se4+O3).H2O
Hydrated selenite of lead
Crystal system: Triclinic
Specific gravity: 5.66 calculated
Streak: White
Colour: Colourless to white
Luminescence: No fluorescence under UV
Environments
Localities
At the type locality, the Baccu Locci Mine, Villaputzu, South Sardinia Province, Sardinia, Italy, the ore mainly
consists of galena and
arsenopyrite, with accessory minerals
sphalerite, chalcopyrite,
pyrite and pyrrhotite.
In the oxidation zone there is a notable concentration of
secondary minerals, mainly
anglesite, azurite,
brochantite and gypsum, with minor
linarite, together with subordinate amounts of several other species,
including atacamite, bayldonite,
beaverite,
carbonate-cyanotrichite,
chalcoalumite,
chalcophyllite,
chlorargyrite, devilline,
olivenite, osarizawaite,
pseudoboleite, pyromorphite,
serpierite, smithsonite,
spangolite, native sulphur,
vanadinite and wulfenite.
addition, there is a local concentration of selenites, especially
chalcomenite.
Orlandiite occurs in these chalcomenite-rich concentrations as very
small elongate tabular crystals, up to 0.1 mm in length, which are colourless to white, and in places associated with
lemon-yellow aggregates, up to 0.1 mm across, of platy crystals of another new phase. These are generally found together
with chlorides, such as green atacamite or very small small dark blue cubes
of pseudoboleite or, much more rarely, with
chlorargyrite of an unusual pale pink colour. In the same association,
there are several other selenium oxysalts, all in very minor amounts compared
with chalcomenite, which is by far the most abundant
selenium-rich mineral here. Among these oxidised
selenium-bearing minerals there are elongate bundles of
olsacherite or, much more rarely,
mandarinoite, in small spherical aggregates of prismatic yellowish green
crystals. At the outermost part of the selenium-rich concentrations,
blue crystals of schmiederite were found, in cases closely resembling
linarite, or francisite in earthy
green masses. No clinochalcomenite has ever been found at the
locality, and in spite of the presence of lead and the
selenite ion, no molybdomenite
has yet been identified in this association.
Orlandiite forms elongate tabular crystals that are invariably twinned
(CM 37.6.1493-1498).
Orlandiite from the Baccu Locci Mine -
Image
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