VONSENITE

    Class : Carbonates, nitrates, borates
    Subclass : Borates
    Crystal system : Orthorhombic
    Chemistry : Fe3BO5
    Rarity : Rare

Vonsenite, iron-bearing, forms a continuous series with ludwigite, magnesian. It is found in iron-copper skarns, more rarely tungsten-molybdenum, where it can constitute an industrial source of boron. It is also found in carbonate xenoliths ejected by Italian volcanoes. Vonsenite seems rarer than ludwigite. It was named in honor of the American collector Magnus Vonsne, who donated his collection to the California Academy of Sciences. It is a borate that crystallizes in long, often acicular crystals, greenish-black to black in color, sometimes generating fibrous clusters, and vaguely evokes iron-bearing tourmalines.

Main photo : Vonsenite from La Fossa, Vulcano, Aeolian Islands, Italy © Elmar Lackner

Vonsenite in the World

Its best site is probably Burguillos near Badajoz (Spain), where vonsenite occurs in fibrous masses with axinite, magnetite, uraninite and hematite in an iron skarn. Particularly spectacular fibroradiated masses have been discovered at Brosso (Piedmont, Italy). It is also known in well-formed crystals in the Riverside district (California).

Right photo : Vonsenite from Capranica, Italy © Gianfranco Ciccolini

Vonsenite in France

Vonsenite is not present in the French underground.

Twinning

No twinning known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 5
Density : 4.21
Fracture : Undetermined
Streak : Brown-black

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

Solubility : -

Magnetism : NoneRadioactivity : None