Xenotime - Occurrence

Occurrence

Occurring as a minor accessory mineral, xenotime is found in pegmatites and other igneous rocks, as well as gneisses rich in mica and quartz. Associated minerals include biotite and other micas, chlorite group minerals, quartz, zircon, certain feldspars, analcime, anatase, brookite, rutile, siderite, and apatite. Xenotime is also known to be diagenetic: It may form as minute grains or as extremely thin (less than 10 µ) coatings on detrital zircon grains in siliciclastic sedimentary rocks. The importance of these diagenetic xenotime deposits in the radiometric dating of sedimentary rocks is only beginning to be realised.

Discovered in 1832, xenotime's type locality is Hidra (Hitterø), Flekkefjord, Vest-Agder, Norway. Other notable localities include: Arendal and Tvedestrand, Norway; Novo Horizonte, São Paulo, Novo Horizonte, Bahia, and Minas Gerais, Brazil; Madagascar; and California, Colorado, Georgia, and North Carolina, New Hampshire, United States. A new discovery of gemmy, colour change (brownish to yellow) xenotime has been reported from Afghanistan and been found in Pakistan. North of Mount Funabuse in Gifu Prefecture, Japan, a notable basaltic rock is quarried at a hill called Maru-Yama: Crystals of xenotime and zircon arranged in a radiating, flower-like pattern are visible in polished slices of the rock, which is known as chrysanthemum stone (translated from the Japanese kiku-ishi). This stone is widely appreciated in Japan for its ornamental value.

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 xenotime than the heaviest lanthanides are in monazite.