THOMSENOLITE

    Class : Halides
    Subclass : Fluorides
    Crystal system : Monoclinic
    Chemistry : NaCaAlF6 H2O
    Rarity : Rare


Thomsenolite is a dimorphic fluoride of pachnolite, which occurs mainly in granitic pegmatites, sometimes in rhyolites or in fluorinated pegmatites. It is always a secondary mineral formed by alteration of other fluorides. It was named in honor of Hans Peter Jörgen Thomsen, Professor of Chemistry at the University of Copenhagen and pioneer of the industrial exploitation of cryolite in Greenland. Thomsenolite occurs as prismatic crystals up to 5 cm, often grouped in parallel groups, rarely in pseudocubic individuals, stalactites, spherulites or masses of chalcedony appearance. Thomsenolite is colorless or white, but sometimes reddish or pink due to the inclusion of iron oxides.

Main photo : Thomsenolite from Ivigtut, Greenland © Beppe Finello

Thomsenolite from Ivigtut, Greenland © Elmar Lackner
Thomsenolite from Ivigtut, Greenland © OT. Ljøstad
Thomsenolite from Ivigtut, Greenland © Edgar Müller
Thomsenolite in epitaxy on hydrokenoralstonite from Ivigtut © Gianfranco Ciccolini

Thomsenolite in the World

The most beautiful specimens of thomsenolite were extracted from the famous pegmatite of Ivigtut (Greenland) where it is formed by alteration of cryolite. It is known from several other localities including the pegmatite of St Peter's Dome (Pike's Peak, Colorado), at Miass (Urals, Russia) and in the geodes of the Spider claim rhyolite (Utah) accompanying tridymite and boltwoodite.

Thomsenolite in France

Thomsenolite is not present in the French underground.

Twinning

No known twin for this mineral species. However, some epitaxies can produce crosses.

Fakes and treatments

No fakes listed for this mineral species.



Hardness : 3 to 3.5
Density : 2.981
Fracture : Irregular
Streak : White


TP : Translucent to transparent
RI : 1.407 to 1.415
Birefringence : 0.008
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None


Solubility : Sulfuric acid

Magnetism : NoneRadioactivity : None