xenotime

Xenotime is a rare-earth phosphate mineral, the major component of which is yttrium orthophosphate (YPO4). The phosphate ions are described by a tetrahedral shape and coordinate to the center Y3+ metal ion in a way that closely resembles the structure of zircon (ZrSiO4). It forms a solid solution series with chernovite-(Y) (YAsO4) and therefore may contain trace impurities of arsenic, as well as silicon dioxide and calcium. Other iso-structural ions that undergo exchanges with PO4 are VO4 and NbO4 ions, contributing to the list of possible co-occurring elements that may be in need of separation. The rare-earth elements dysprosium, erbium, terbium and ytterbium, as well as metal elements such as thorium and uranium (all replacing yttrium) are the expressive secondary components of xenotime. Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly radioactive. Lithiophyllite, monazite and purpurite are sometimes grouped with xenotime in the informal "anhydrous phosphates" group. Xenotime is used chiefly as a source of yttrium and heavy lanthanide metals (dysprosium, ytterbium, erbium and gadolinium). Occasionally, gemstones are also cut from the finest xenotime crystals.

== Etymology == The name xenotime is written originally kenotime from the Greek words () 'vain' and () '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 (he named it Thorium, but later understood to be a compound of a previously discovered yttrium). The criticism was blunted, as over time kenotime was misread and misprinted xenotime with the error suggesting the etymology () + () as 'different honor'. Xenotime was first described for an occurrence in Vest-Agder, Norway in 1824.