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The xenotime Mineral Series
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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.
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. |
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Chemical Formula |
General Group Formula: (Y,Yb,Ce,La,Nd,Sc)(PO,VO,SO)4 Xenotime-(Y) Formula: YPO4 |
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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) |
| Variable Formula |
(Y,Th,U,Dy,Yb,Er,Gd)PO4 |
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Color |
Light to dark brown, yellowish-brown, and orange. Also yellow, reddish-brown, and greenish brown. |
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Streak |
White, light yellow, light brown |
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Hardness |
4 - 5 |
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Crystal System |
Tetragonal |
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Crystal Forms
and Aggregates |
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. |
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Transparency |
Translucent to opaque. Transparent in microcrystals. |
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Specific Gravity |
4.4 - 5.1 |
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Luster |
Vitreous, resinous |
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Cleavage |
1,1 |
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Fracture |
Splintery |
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Tenacity |
Brittle |
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Other ID Marks |
Radioactive when containing uranium or thorium |
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In Group |
Phosphates; True Phosphates |
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Striking Features |
Crystal habits, heavy weight, and mode of occurrence. |
| Environment |
Granite pegmatites, and metamorphosed gneiss and schists. |
| Rock Type |
Igneous, Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
1 |
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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.
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Zircon - Higher specific gravity and hardness, poorer cleavage.Anatase - May be very difficult to distinguish, though usually more blue in color and crystals striated.
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