Euxenite

Euxenite
Euxenite from Norway, around 11 cm of size
General
Category	Oxide minerals
Formula (repeating unit)	(Y,Ca,Ce,U,Th)(Nb,Ta,Ti) 2O 6
IMA symbol	Eux
Strunz classification	4.DG.05
Crystal system	Orthorhombic
Space group	Pcmn (no. 62)
Identification
Color	Black, brownish black, greenish black
Crystal habit	Massive, anhedral crystals in matrix
Twinning	Common on [201]
Cleavage	None
Fracture	Conchoidal to subconchoidal
Mohs scale hardness	5.5 to 6.5
Luster	Brilliant submetallic, waxy to resinous on fractures
Streak	Yellowish, grayish, or reddish brown
Diaphaneity	Opaque, translucent on thin edges
Specific gravity	4.7 to 5
Optical properties	Isotropic
Refractive index	n = 2.06 – 2.24
Other characteristics	Metamict – originally crystalline, now amorphous due to radiation damage. Radioactive
References

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 (εいぷしろんὔξενος), hospitable or friendly to strangers, in allusion to the many rare elements that it contains.

Occurrence

It occurs in granite pegmatites and detrital black sands.

It is found in many locations worldwide, notably its type locality in Jølster, Sunnfjord, Norway. 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.

Use

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