Euxenite

(repeating unit)(Y,Ca,Ce,U,Th)(Nb,Ta,Ti)
₂O
₆IMA symbolEux^[1]Strunz classification4.DG.05Crystal systemOrthorhombicSpace groupPcmn (no. 62)IdentificationColorBlack, brownish black, greenish blackCrystal habitMassive, anhedral crystals in matrixTwinningCommon on [201]CleavageNoneFractureConchoidal to subconchoidalMohs scale hardness5.5 to 6.5LusterBrilliant submetallic, waxy to resinous on fracturesStreakYellowish, grayish, or reddish brownDiaphaneityOpaque, translucent on thin edgesSpecific gravity4.7 to 5Optical propertiesIsotropicRefractive indexn = 2.06 – 2.24Other characteristicsMetamict – originally crystalline, now amorphous due to radiation damage. RadioactiveReferences^[2][3][4]

Euxenite, or euxenite-(Y) (the official mineralogical name), is a brownish black mineral with a metallic luster.

Chemistry

It contains calcium, niobium, tantalum, cerium, titanium, yttrium, and typically uranium and thorium, with some other metals. The chemical formula is (Y, Ca, Ce, U, Th)(Nb, Ta, Ti
₂)O
₆. It is commonly partially amorphous due to radiation damage.

Euxenite forms a continuous series with the titanium rich polycrase-(Y) having the formula (Y,Ca,Ce,U,Th)(Ti,Nb,Ta)
₂O
₆.

Name and discovery

It was first described in 1870 and named for from the Greek (εὔξενος), hospitable or friendly to strangers, in allusion to the many rare elements that it contains.^[4][3]

Occurrence

It occurs in granite pegmatites and detrital black sands.^[2]

It is found in many locations worldwide, notably its type locality in Jølster, Sunnfjord, Norway.^[3] Other locations include the Ural Mountains of Russia; Sweden; Minas Gerais, Brazil; Ampangabe, Madagascar; Ontario, Canada; and in Arizona, Wyoming and Colorado in the US.^[5]

Use

Euxenite is used as an ore of the rare earth elements it contains. Rare large crystals have also been used in jewelry.^[5]

References