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Formula: FeSe2
Selenide, marcasite group,
paramorph of dzharkenite
Crystal System: Orthorhombic
Specific gravity: 7.20 measured, 7.139 calculated
Hardness: 6 to 6½
Streak: Black
Colour: Steel grey to tin white with rose tint, brass yellow
Common impurities: Co
Environments
Ferroselite occurs in red-bed deposits of the Colorado Plateau type. Associated minerals include
uraninite, pyrite,
marcasite, chalcopyrite,
sphalerite, selenium,
clausthalite, cadmoselite,
bornite, cobaltomenite,
laumontite and baryte
(HOM, Mindat).
Localities
At the Tumiñico Mine, Sierra de Cacho, Villa Castelli, General Lamadrid department, La Rioja Province, Argentina,
brodtkorbite occurs in a
selenide vein-type assemblage that also contains
berzelianite, bellidoite,
cadmoselite, chaméanite,
crookesite, eskebornite,
eucairite, ferroselite,
hakite, klockmannite,
trogtalite-krut'aite,
tiemannite, tyrrellite,
umangite and uraninite.
It appears that in the the first stage of selenide mineralisation the
crystallisation of ferroselite was followed by tyrrellite and
cobalt-rich members of the
trogtalite-krut'aite solid
solution series and ended with several as yet undefined mineral species.
The second stage began with the formation of hakite,
cadmoselite and several as yet undefined phases, and terminated with
the deposition of bukovite and
chaméanite. These two minerals replace the earlier-formed
cadmoselite, but, in turn, were replaced by
umangite.
In the third stage umangite is the most widespread species and is
generally associated with klockmannite.
Berzelianite and bellidoite
are less common; crookesite is very rare and is commonly found embedded
in berzelianite.
Brodtkorbite is generally intimately associated with
berzelianite.
Cross-cutting veinlets of tiemannite in
brodtkorbite grains mark the beginning of the fourth stage of
mineralisation, during which various selenides were deposited, including
eucairite, naumannite and
tiemannite.
The fifth and last stage of ore formation involved the precipitation of sulphides in negligible amounts,
particularly chalcopyrite,
bornite, chalcocite and
covellite.
Secondary minerals, such as
malachite, chalcomenite,
schmiederite and
connellite, are usually observed in vugs and cavities of the
calcite gangue
(CM 40.225-237).
At the type locality, the Ust' Uyok deposit, Turan District, Tuva, Russia, ferroselite occurs with minor
chalcopyrite and pyrite cementing
sandstone and pelites (sedimentary rocks composed of
clay or mud-sized particles)
(AM 41.671).
At a number of mines in the Uravan district, Montrose county, Colorado, USA, ferroselite occurs in
uranium-vanadium ores in
sandstone, with
coalified wood
(HOM).
At several localities on the Colorado Plateau, Utah, USA, ferroselite occure in red-bed deposits of the Colorado
Plateau type,
peripheral to pyrite and uranium
concentrations
(HOM).
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