SELENIUM

    Class : Elements
    Subclass : Non-metals
    Crystal system : Trigonal
    Chemistry : Se
    Rarity : Rare

Native selenium is a rare mineral from uranium deposits and coal mines. In this second type of occurrence, it occurs in rare small flexible acicular crystals, gray-black in color and metallic luster. In its most common facies, it is a product of atmospheric alteration of selenides (more particularly clausthalite). It accompanies uranium minerals on which it forms incrustations and dull reddish-black masses, turning bright red when in powder form. Its name comes from the Greek Selênê (Moon) by analogy with Tellurium, itself named after the Latin Tellus (Earth).

Main photo : Native selenium from Glen Lyon, Pennsylvania, USA © Gianfranco Ciccolini

Searlesite from Coaldale Mining District, Nevada, USA © Gianfranco Ciccolini
Twinned supposed searlesite from Rio Tinto, California, USA © Gianfranco Ciccolini
Twinned supposed searlesite from Rio Tinto, California, USA © Jason B. Smith
Searlesite on aegyrine from Point of Rocks Quarry, New-Mexico, USA © Jerry Cone

Selenium in the World

The best specimens of native selenium come from a fiery pyritic deposit : the United Verde Mine near Jerome (Arizona), and from the fiery coal mines of Glen Lyon (Pennsylvania). Good millimeter crystals come from German coal mines, notably the Anna mine near Cologne. Selenium is also present in American uranium sandstones from Colorado and South Dakota in particular. It is found in the fumaroles of the Lipari Islands (Italy), and in the surprising selenide vein of Pacajake, near Colquechaca (Bolivia).

Selenium in France

In France, reddish powdery selenium, resulting from the alteration of selenides and known in the pitchblende vein of Chaméane (Puy-de-Dôme). It is also described in Olloix (Puy-de-Dôme), at the Clausis mine near St-Véran (Hautes-Alpes) and at Traou ar Ru near Lannion (Côtes-d'Armor).

Twinning

No twinning known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 2
Density : 4.8
Fracture : Undertermined
Streak : Red

TP : Opaque
RI : 3.000 to 4.040
Birefringence : 1,040
Optical character : Uniaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None