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Formula: Cu6BiSe4(Se2)
Sulphosalt, bismuth- and selenium-
bearing mineral
Crystal System: Orthorhombic
Specific gravity: 6.76 calculated
Hardness: 3½
Streak: Brownish black
Colour: Brownish to light maroon
Environments
Localities
At the type locality, El Dragón mine, Porco Municipality, Antonio Quijarro Province, Potosí, Bolivia,
eldragónite is a widespread constituent of the selenide assemblage
and is invariably included in chemically zoned kruťaite in a
low-temperature hydrothermal vein-type deposit.
Eldragónite seems to be more common in those types of kruťaite ore
that have undergone a late event of brittle deformation, causing
brecciation. Subsequent infiltration of fluids containing
bismuth, lead and
mercury led to the precipitation of
clausthalite,
watkinsonite, petrovicite
and related unnamed phases.
Eldragónite can be found concentrated in random sections of kruťaite
crystals where these are embedded in a carbonate gangue. Commonly
aggregates of eldragónite grains replace a cobalt-rich member of the
series trogtalite –
penroseite – kruťaite.
Eldragónite is commonly associated with watkinsonite;
petrovicite is less common.
Clausthalite is next in abundance after
kruťaite, and commonly observed as a network penetrating the hosting
kruťaite; watkinsonite and
petrovicite occasionally can be found embedded in this veining of
clausthalite;
klockmannite and umangite
are fairly abundant; tiemannite was detected only once.
Native gold can be detected in almost every section.
Sulphide minerals, including chalcopyrite,
pyrite, marcasite and
covellite, predate the selenium
mineralisation. Traces of native selenium and various
secondary phases such as
goethite, chalcomenite,
olsacherite, schmiederite,
cobaltomenite and
ahlfeldite, are ubiquitous in the oxidised material
(CM 50.282-294).
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