Berthierite - Encyclopedia

    Class : Sulfides and sulfosalts
    Subclass : Sulfosalts
    Crystal System : Orthorhombic
    Chemistry : FeSb₂S₄
    Rarity : Fairly common

Berthierite is an iron and antimony sulphide found in low and medium temperature hydrothermal veins, in common association with quartz, baryte and stibnite. It was named in honor of the French chemist Pierre Berthier who was the first to study this mineral. The free crystals are elongated, frequently acicular, striated longitudinally according to [001]: they remain however exceptional and very rarely exceed the centimeter. Berthierite usually occurs in fibrous masses (more common than for stibnite), feathery or radiate up to 6 cm in radius, or in grainy masses. When fresh, berthierite has a steel-gray color similar to stibnite, but it quickly becomes iridescent and dulls in air, sporting a bronze patina that browns over time. Berthierite easily oxidizes at outcrops to a mixture of antimony and iron oxides ("chocolate" oxides) which usually retain the fibrous appearance of the replaced mineral. Berthierite is an antimony ore less appreciated than stibnite because of its lower content of this metal (57% against 72%) and its more difficult roasting.

Main photo : Berthierite from Herja, Mamures, Romania © Lopatkin Oleg

No known twin for this mineral species.

This mineral can be confused with the stibine with which it shares deposits. Some unscrupulous Asian sellers also call carborundum (synthetic silicon carbide) berthierite to make it easier to sell.