GEOCRONITE

    Class : Sulfides and sulfosalts
    Subclass : Sulfosalts
    Crystal system : Monoclinic
    Chemistry : Pb14(Sb,As)6S23
    Rarity : Uncommon

Geocronite is an uncommon lead sulfoantimonide, occurring in low-temperature hydrothermal veins along with galena, sphalerite, pyrite, tetrahedrite and barite. It forms a continuous series with jordanite, its arseniferous equivalent. It takes its name from the Greek gê (Earth) and Cronos (Saturn), ancient alchemy terms designating antimony and lead. Geocronite gives rare tabular crystals, sometimes large (9 cm), commonly twinned in sectors, and grainy to earthy masses of lead gray to grayish color.

Main photo : 6.5 cm geocronite Pollone Mine, Tuscany, Italy © Marco Barsanti

Geocronite from Fantiscritti, Tuscany, Italy © Gianfranco Ciccolini
Geocronite from Borgofranco Mines, Piedmont, Italy © Franco Luca Bonino
Geocronite from Carrara, Tuscany, Italy © Stephan Wolfsried
Twinned geocronite from Silver Tunnel, British Columbia, Canada © Stephan Wolfsried

Geocronite in the World

Beautiful geocronite crystals are known in Italy (Serravezza) and in Xanda, near Virgem da Lapa (Minas Gerais, Brazil) where probably the most beautiful specimens come from. But there are numerous deposits that have provided beautiful specimens in Mexico (Noche Buena), Russia (Nerchinsk), Sweden (Falun) and Canada (Hemlo).

Geocronite in France

In France, decimetric clusters of twinned geocronite were extracted from the barite and semseyite vein of Deveix, near Bort-les-Orgues (Corrèze). It is also reported in Farges (Corrèze), Bournac (Hérault), Péone (Alpes-Maritimes) and at the Cougnasses Mine near Orpierre (Hautes-Alpes).

Twinning

Twin is known on {001}, it can be multiple and form stars.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2.5 to 3
Density : 6.46
Fracture : Irregular
Streak : Gray

TP : Opaque
RI : -
Birefringence : -
Optical character : -
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric acid


Magnetism : None
Radioactivity : None