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Formula: Cu3Bi(Se4+O3)2O2Cl
Valence: Cu2+3Bi3+(Se4+O3)2O2Cl
Selenite of copper and
bismuth
Crystal system: Orthorhombic
Specific gravity: 5.42 calculated
Hardness: 3 to 4
Streak: Pale apple green
Colour: Bright green
Environments
Francisite is a rare secondary mineral; associated
minerals include baryte,
chorargyrite, muscovite,
naumannite, bismuth,
djurleite and Cu–Bi–Ag selenides
(HOM).
Localities
At the type locality, the Iron Monarch Main Pit, Iron Knob, Pastoral Unincorporated Area, South Australia,
francisite was found in cavities at the core of an isolated lens of
baryte within massive hematite ore.
In addition to baryte, the minerals associated with francisite include
chlorargyrite, which occurs as hexagonal prisms, and fine-grained
white muscovite. Also present are
naumannite, native bismuth,
djurleite, and several poorly defined
copper, silver and
bismuth selenides, all of which
occur as small blebs within the baryte. Francisite occurs as radiating
clusters and groups of bladelike crystals up to 0.25 mm in length on baryte
crystals and in hollows in the fine-grained muscovite that fills many of
the cavities within the baryte.
Iron Monarch is a large sedimentary iron ore deposit where the principal ore mineral is
hematite; The upper part of
the deposit also contains large lenses of manganese oxides, principally
hausmannite. Small amounts of other unusual
secondary minerals, mainly phosphates, have also been found in
isolated areas within the ore body
(AM 75.1421-1425).
Francisite from the Iron Monarch Main Pit -
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