RALSTONITE

    Class : Halides
    Subclass : Oxyfluorides
    Crystal system : Cubic
    Chemistry : NaxMgxAl2-x(F,OH)6 H2O
    Rarity : Rare

Ralstonite (or hydrokenoralstonite) is a rare fluoride of fluorinated pegmatites and associated greisens, sometimes associated with hydrothermal veins of tin or molybdenum, and exceptionally carbonatite. It was named in honor of Reverend J. Grier Ralston of Norristown who first observed the mineral at Ivigtut, Greenland. Ralstonite forms small octahedra or cubes, less frequently cubo-octahedra, colorless or white, but often superficially tinged yellowish by iron oxides. Ralstonite is associated with other pegmatite fluorides (elpasolite, thomsenolite, cryolite, fluorite, etc...).

Main photo : Ralstonite from Ivigtut Mine, Greenland © OT. Ljøstad

Ralstonite from Ivigtut Mine, Greenland © Italo Campostrini
Ralstonite from Clara Mine, Germany © Joy Desor
Ralstonite & pachnolite from Ivigtut Mine, Greenland © Volker Betz
Ralstonite from Ivigtut Mine, Greenland © Luigi Mattei

Ralstonite in the World

The most beautiful ralstonite octahedra measure up to 1 cm and were found in the famous pegmatite of Ivigtut (Greenland). Small crystals of 1 mm have been recovered from the pegmatite of Pike's Peak (Colorado) where it encrusts pachnolite crystals and occupies cavities in pachnolite and thomsenolite, and in that of Lake Gjerdingen (Norway). Among its other deposits, ralstonite is known in several tin mines such as Colquiri (Bolivia) and Mount Cleveland (Australia), in the Russian molybdenum mine of Zharchikhinsk in eastern Siberia. More surprisingly, it is also described in the antimoniferous limestones of Cetine (Tuscany, Italy).

Ralstonite in France

In France, ralstonite was described in the Piton de la Fournaise massif in Réunion.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 5
Density : 2.56 to 2.62
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.399 to 1.427
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : None

Solubility : Sulfuric acid

Magnetism : NoneRadioactivity : None

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