Euxenite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Orthorhombic
    Chemistry : (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)₂O₆
    Rarity : Very rare

Euxenite is primarily a mineral of granites and granitic pegmatites, as well as pegmatites associated with nepheline syenites. It is a complex oxide of titanium, tantalum and niobium, which forms a series with polycrase, where titanium dominates. Substitutions between elements are numerous, and euxenite is frequently rich in uranium, thorium and less common rare earths (dysprosium, erbium or ytterbium). Although frequently metamict, it is a very resistant mineral which concentrates well in alluvium. Its name comes from the Greek eu (good) and xenos (foreign) due to the large number of rare elements used in its composition. Euxenite appears in stocky prisms, sometimes flattened, with faces frequently striated longitudinally. They are often gathered in parallel or subparallel groups, slightly radiate or flabelliform ; they also form metamict masses. Euxenite is reddish-brown or dark brown to black in color, but this is often masked by a thin crust of alteration (metamictization) of light yellowish brown. The conchoidal break reveals a tarry appearance, very characteristic of the mineral. Euxenite from Malagasy deposits was exploited as uranium and radium ore at the beginning of the century. Heavy Ilsenite sands remain potential rare earth and thorium ores.

Main photo : Euxenite from Betsiboka, Madagascar © Knut Eldjarn

Twins are known on {201} and common (flattened and striated). Perhaps present on {101} and {013} but rare.

No fake listed for this mineral species.