Xenotime

Xenotime is a mineral species in the phosphate group, best known for the yttrium phosphate end member YPO4. The xenotime group forms a solid solution series in which yttrium can be partially or largely replaced by other rare-earth elements such as dysprosium, erbium, ytterbium, and others. In practice, xenotime-(Y) denotes the yttrium-dominant end member, while other end members are named as xenotime-(REE) with the dominant rare-earth cation in parentheses.

Xenotime occurs in igneous rocks, particularly granitic pegmatites, and in hydrothermal veins. It is commonly found as a late-stage accessory mineral and frequently coexists with zircon, monazite, apatite, and other rare-earth-bearing minerals. The mineral can form euhedral to subhedral prismatic crystals or occur as disseminated grains within silicate rocks.

Crystallography and appearance: Xenotime crystallizes in the tetragonal system. It typically forms elongated prismatic crystals and grains that range in color from yellow-brown to brown, sometimes greenish, and it has a resinous to adamantine luster. The mineral is relatively hard and brittle, with a distinct crystal structure that allows it to be distinguished from other phosphate minerals in hand specimen and under the microscope.

Economy and extraction: Because xenotime concentrates yttrium and other rare-earth elements, it can be an important ore mineral in deposits where REEs are sought. Processing aims to separate xenotime concentrates from other REE-bearing minerals such as monazite and zircon, after which yttrium oxide and other rare-earth oxides are recovered.

Summary: Xenotime is a rare-earth phosphate mineral with a yttrium-dominant end member and a family of rare-earth substitutions. It forms in granitic and hydrothermal environments, crystallizes in the tetragonal system, and holds economic value as a source of yttrium and other rare earth elements.