Ferroselite

ferroselite

cobaltomenite

clausthalite

cadmoselite

Images

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

Sedimentary 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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