Aeschynite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal System : Orthorhombic
    Chemistry : (Ce,Ca,Fe,Th)(Ti,Nb)2(O,OH)6
    Rarity : Very rare

Aeschynite is now considered a group of complex oxides of titanium and niobium, subdivided into three minerals according to the dominant metal : aeschynite-(Ce), aeschynite-(Nd) and aeschynite-(Y). Its name comes from the Greek aeschyne (shame) because when it was discovered in 1828, chemists were unable to separate all its constituents. Aeschynite is a rare oxide of nepheline syenites, and more generally of alkaline syenites, more rarely of carbonatites and granitic pegmatites. Very resistant to weathering, it concentrates well in the placers. It is a black to yellow-brown mineral, often radioactive due to the fairly common presence of thorium (up to 30% ThO2), its crystals are striated, prismatic to tabular. It is a potential ore of thorium, tantalum, niobium and rare earth elements

Main photo : Aeschynite-(Y) from Luserna Stone Quarries, Turin, Piedmont, Italy - © Giuseppe Finello 

12 cm aeschynite-(Y) from Clora May Mine, Colorado, USA © Juan Jimenez
Aeschynite-(Y) from Furka basis tunnel, Valais, Switzerland © Stephan Wolfsried
Aeschynite-(Y) from Mätti Valley, Valais, Switzerland © Stephan Wolfsried
Aeschynite-(Y) on dolomite from Trimouns, Ariège, France © Michel Bretheau

Aeschynite in the World

Aeschynite is abundant in the nepheline syenites of the Ural Mountains (Russia), around Miass and Zlatoust. Aeschynite is also common in the alkaline massifs of southern Norway (Arendal) where aeschynite-(Y) crystals can exceed 10 cm, as in the carbonatite of Darby (Montana) and in Clora May Mine (Colorado).

Aeschynite in France

Aeschynite-(Y) is present in France in microcrystals in certain alpine fissures, notably at Plan-du-Lac (Isère) associated with anatase, at the Grand Pic and the Pointe du Rozet (Savoie), in the Madone valley. des Fenestres (Alpes-Maritimes) and in the talc quarry of Trimouns (Ariège).

Twinning

No known twin for this mineral species.

Fakes and treatments

No known fakes or treatments.



Hardness : 5 to 6
Density : 5,19
Fracture : Conchoidal
Trace : Black to brown




TP : Translucent to opaque
RI : 2,26
Birefringence : Not measurable
Optical character : -
Pleochroism : None
Fluorescence : None


Solubility : Hydrochloric and sulfuric acids

Magnetism : Paramagnetic
Radioactivity : None

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