Xenotime

Xenotime is a rare earth phosphate mineral, whose major component is yttrium orthophosphate (YPO₄). 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. The rare earths dysprosium, erbium, terbium, and ytterbium, and metal elements like 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 finer xenotime crystals.