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The xenotime Mineral Series

Rocket Shaped Xenotime with Rutile

Xenotime describes a group of several closely related phosphates, arsenates, and vanadates composed of rare earth elements. The term is generally used to describe the most common member of the group, Xenotime-(Y), which is the yttrium phosphate end member of this series. Other, rarer members of the Xenotime series include Xenotime-(Yb), Cherovite, and Wakefieldite.

Xenotime may contain radioactive elements in its structure, and therefore may have some level of mild radioactivity. It frequently forms together with Zircon, and may even grow together in the same crystals as epitaxial overgrowths.

The name Xenotime is derived from an odd source. Its name was given by French mineralogist François Sulpice Beudant after the Greek words "Xenos" meaning stranger, and "Time" meaning honor, to debunk the theory proposed by chemist Jacob Berzelius that the yttrium in this mineral is in fact a new, undocumented element.

Chemical Formula

General Group Formula: (Y,Yb,Ce,La,Nd,Sc)(PO,VO,SO)₄

Xenotime-(Y) Formula: YPO₄

Color

Light to dark brown, yellowish-brown, and orange. Also yellow, reddish-brown, and greenish brown.

Crystal System

Tetragonal

Properties

Streak
White, light yellow, light brown

Hardness
4 - 5

Transparency
Translucent to opaque. Transparent in microcrystals.

Specific Gravity
4.4 - 5.1

Luster
Vitreous, resinous

Cleavage
1,1

Fracture
Splintery

Tenacity
Brittle

Other ID Marks
Radioactive when containing uranium or thorium

Crystal Habits

In prismatic crystals, usually with pyramidal terminations, sometimes in stepped pyramids. Often bipyramidal, and occasionally twinned. Also radial, dipyarmidal (resembling elongated octahedrons), massive, and grainy.

3D Crystal Atlas

Additional Information

Composition
Xenotime Group: Phosphate, vanadate, or arsenate of yttrium, ytterbium, cerium, lanthanum, neodymium, or scandium

Xenotime-(Y): Yttrium phosphate, sometimes with thorium and uranium, as well as the lanthanide metals (dysprosium, ytterbium, erbium and gadolinium)

In Group
Phosphates; True Phosphates

Striking Features
Crystal habits, heavy weight, and mode of occurrence.

Environment
Granite pegmatites, and metamorphosed gneiss and schists.

Rock Type
Igneous, Metamorphic

Uses

As an ore of yttrium.

Noteworthy Localities

Outstanding crystals of Xenotime, in in large, chocolate-brown crystals (which can resemble rockets) and have Rutile inclusions come from Ibitiara (Novo Horizonte), Bahia, Brazil. Another exceptional locality, that has produced some of the largest crystals of this mineral in prismatic orange crystals, is Zagi Mountain, Peshawar, Pakistan.

Dipyramidal Xenotime crystals have come from the granite pegmatites of Aust-Agder and Vest-Agder, Norway, especially at the Evje-Iveland pegmatite field. Small prismatic crystals with pyramidal terminations were found in a Graphite mine in Amstall, near Mühldorf, Carinthia, Austria.

In the U.S., small, dark brown Xenotime crystals in matrix come from the Big Bertha Mine, Jefferson Co., Colorado; and large crude crystals were found in Clora May Mine, near Buena Vista, Chaffee Co., Colorado. Historical crystals from late 1800's were found in pegmatites on Manhattan Island, New York Co., New York.