The name xenotime is from the Greek words kenós (κενός) 'vain' and timē (τιμή) 'honor', akin to 'vainglory'. It was coined by French mineralogist François Sulpice Beudant as a rebuke of another scientist, Swedish chemist Jöns Jacob Berzelius, for the latter's premature claim to have found in the mineral a new chemical element (later understood to be previously discovered yttrium). The criticism was blunted, as over time kenotime was misread and misprinted xenotime[2][3][5] with the error suggesting the etymology xénos (ξένος) + timē (τιμή) as 'different honor'. Xenotime was first described for an occurrence in Vest-Agder, Norway in 1824.[3]
Properties
Crystallising in the tetragonal (I41/amd) crystal system, xenotime is typically translucent to opaque (rarely transparent) in shades of brown to brownish yellow (most common) but also reddish to greenish brown and gray. Xenotime has a variable habit: It may be prismatic (stubby or slender and elongate) with dipyramidal terminations, in radial or granular aggregates, or rosettes. A soft mineral (Mohs hardness 4.5), xenotime is—in comparison to most other translucent minerals—fairly dense, with a specific gravity between 4.4–5.1. Its lustre, which may be vitreous to resinous, together with its crystal system, may lead to a confusion with zircon (ZrSiO4), the latter having a similar crystal structure and with which xenotime may sometimes occur.
Xenotime has two directions of perfect prismatic cleavage and its fracture is uneven to irregular (sometimes splintery). It is considered brittle and its streak is white. The refractive index of xenotime is 1.720–1.815 with a birefringence of 0.095 (uniaxial positive). Xenotime is dichroic with pink, yellow or yellowish brown seen in the extraordinary ray and brownish yellow, grayish brown or greenish brown seen in the ordinary ray. There is no reaction under ultraviolet light. While xenotime may contain significant amounts of thorium or uranium, the mineral does not undergo metamictization like sphene or zircon would.
Small tonnages of xenotime sand are recovered in association with Malaysian tin mining, etc. and are processed commercially. The lanthanide content is typical of "yttrium earth" minerals and runs about two-thirds yttrium, with the remainder being mostly the heavy lanthanides, where the even-numbered lanthanides (such as Gd, Dy, Er, or Yb) each being present at about the 5% level, and the odd-numbered lanthanides (such as Tb, Ho, Tm, Lu) each being present at about the 1% level. Dysprosium is usually the most abundant of the even-numbered heavies, and holmium is the most abundant of the odd-numbered heavies. The lightest lanthanides are generally better represented in monazite while the heaviest lanthanides are in xenotime.