Euxenite
Euxenite is a complex oxide mineral with the chemical formula (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6. It is a radioactive mineral belonging to the euxenite-polycrase series.
Properties: Euxenite is typically black or dark brown in color, sometimes with a yellowish or reddish tint due to alteration. It has a vitreous to greasy luster and a subconchoidal to uneven fracture. The mineral is metamict, meaning its crystal structure has been destroyed by radiation damage from its own radioactive elements (uranium and thorium). This metamictization can lead to variations in its density and hardness. Its hardness varies depending on the degree of metamictization, typically ranging from 5.5 to 6.5 on the Mohs scale. The specific gravity ranges from 4.5 to 5.9.
Composition: Euxenite is a complex oxide containing rare earth elements (REEs) such as yttrium, cerium, and sometimes erbium, along with calcium, uranium, thorium, niobium, tantalum, and titanium. The relative proportions of these elements can vary significantly.
Occurrence: Euxenite is found primarily in granite pegmatites and, less frequently, in placer deposits derived from these pegmatites. It is typically associated with other rare earth minerals, such as monazite, xenotime, and allanite. Notable occurrences include Norway, Sweden, Russia (Ural Mountains), Brazil, Madagascar, Canada, and the United States (various locations).
Uses: Euxenite is a source of rare earth elements, niobium, tantalum, uranium, and thorium. Although it is radioactive, its primary value lies in the extraction of the other valuable elements.
Identification: Euxenite is often identified by its color, luster, radioactivity, and association with pegmatites. X-ray diffraction is commonly used to confirm its identity, although metamictization can complicate this process.
Related Minerals: Euxenite forms a series with polycrase-(Y), which is the yttrium-dominant endmember. Other related minerals include columbite-tantalite, fergusonite, and samarskite.