THE MINERAL XENOTIME

Chemistry: YPO4, Yttrium Phosphate
Class: Phosphates
Uses: As mineral specimens and as a source of yttrium.
Specimens

Xenotime is one of the very few minerals, let alone words, that starts with the letter X; a good word to remember in some word games. It is a widely spread mineral throughout the world although good crystals and therefore specimens are somewhat hard to find.

It is one of the few yttrium minerals known to science. Wakefieldite and chernovite-(Y) are other yttrium minerals, although a vanadate and an arsenate respectively. Often uranium or other rare elements such as erbium, thorium, ytterbium, zirconium and the not so rare calcium are found as traces in xenotime replacing the yttrium. Due to the presence of at least some of these radioactive elements, xenotime is frequently slightly radioactive.

Xenotime also will contain traces of silicon dioxide and arsenate replacing the phosphate anion. In fact it forms a solid solution series with the previously mentioned chernovite-(Y) whose formula is YAsO4. It is unusual to have a solid solution series involving the principle anions but it is not as complete a solid solution series as the more famous pyromorphite-vanadinite-mimetite series. That is a more complex phosphate-vanadate-arsenate series.

Also of note is that xenotime is one of the few phosphate minerals that does not contain water molecules, hydroxides or chlorides. It belongs to an informal group of phosphates and called the anhydrous phosphates along with monazite, purpurite and lithiophyllite.

The crystals of xenotime are similar to zircon and can easily be confused with the duller lustered, less transparent samples of zircon. However, the cleavage and the softness of xenotime are sufficient to distinguish them.

PHYSICAL CHARACTERISTICS:

Color is most commonly various shades of brown but also gray, greenish brown, muted red and yellow.
Luster is vitreous to resinous.
Transparency: Crystals are translucent to opaque.
Crystal System is tetragonal; 4/m 2/m 2/m
Crystal Habits include stubby to elongated prismatic crystals that are terminated by variously slanted dipyramids. Also known for nice rosette and radial aggregates.
Cleavage is perfect in two prismatic directions.
Fracture is uneven.
Hardness is 4 - 5
Specific Gravity is approximately 4.4 - 5.1 (heavy for translucent minerals)
Streak is pale brown to yellow or red.
Other Characteristics: Trace amounts of uranium and other rare earth elements may render crystals slightly radioactive.
Associated Minerals are quartz, micas especially biotite, monazite and some feldspars.
Notable Occurrences include Arendal, Hittero and Tvedestrand, Norway; Madagascar; several locations in Brazil and also in the United States in Colorado, California, Georgia and North Carolina.
Best Field Indicators are color, crystal habit, cleavage, softness and luster.

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XENOTIME specimens:
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XENOTIME specimen xen-1
$ 120.00

Dims: 1.0" x 0.3" x 0.3"

Wt: 3.6 g

Ibitiara, Bahia, Brazil

This simple specimen consists of a single crystal of Xenotime, a rather rare yttrium mineral. It has reasonably good tetragonal prismatic form with well-defined edges and faces, and shows a bright, almost vitreous luster. It has a brown color with gold highlights, and is transparent in some areas, though it is mostly translucent, due to heavy internal fracturing. Its form and even the flaws inherent in its form remind me of zircon's.

xen-1 ($120.00)

Ibitiara, Bahia, Brazil

XENOTIME specimen xen-2
$ 170.00

Dims: 1.0" x 0.6" x 0.3"

Wt: 5.6 g

Ibitiara, Bahia, Brazil

This Xenotime specimen consists of a cluster of 3 different crystals. Two of the crystals are broken and incomplete, but the third is intact and has dimensions of 1.0 x 0.3 x 0.3" (2.5 x 0.8 x 0.8 cm). It has a good tetragonal prismatic form with clean faces and well-defined edges, and shows a bright, almost adamantine luster. Its color is a moderately dark brown that shows golden highlights when light is reflected off of its many tiny internal fractures. They show only dim translucence in some areas, though they are each transparent for a very small depth into each crystal. There is no host rock or any other foreign material. This may be the only Xenotime specimen that we get for a little while- they are not easy to come by.

xen-2 ($170.00)

Ibitiara, Bahia, Brazil

XENOTIME specimen xen-3
$ 50.00

Dims: 0.7 x 0.3 x 0.3" (1.8 x 0.8 x 0.8 cm)

Wt: 4.4 g

Ibiajara, Bahia, Brazil

This small thumbnail specimen consists of a single tetragonal prismatic Xenotime crystal. This crystal is in excellent condition, showing very little human-induced damage, and has a good but interrupted form, with edges that are mostly well-defined and faces that are generally clean and show a bright pearly luster. The termination, however, is not completely formed (see the close-up image), probably due to its intersection with a crystal that has since been removed. The Xenotime has the standard brown coloration with golden highlights and shows a dim translucence, especially around its edges. Close examination of the crystal's prism faces will show that there are fibrous needles of rutile trapped just under some of their surfaces. There is no host rock present on this specimen.

xen-3 ($ 50.00)

Ibiajara, Bahia, Brazil

XENOTIME specimen xen-4
$ 115.00

Dims: 1.2 x 0.3 x 0.3" (3.0 x 0.8 x 0.8 cm)

Wt: 0.25 oz. (7.3 g)

Piata Mine, Bahia, Brazil

This small thumbnail specimen consists of a single tetragonal prismatic Xenotime crystal. This crystal shows only minor damage and has excellent form, with well-defined edges and clean faces that possess a bright pearly-to-vitreous luster. Its color is a moderately deep brown with golden highlights, and it is translucent to dimly transparent around its edges. However, there are patches of the surface material that are noticeably transparent a few millimeters down into the crystal. This transparence allows one to see a few rutile needles that permeate the crystal in different areas. There is no host rock present on this piece.

xen-4 ($115.00)

Piata Mine, Bahia, Brazil

XENOTIME specimen xen-5
$ 105.00

Dims: 1.1 x 0.4 x 0.4" (2.8 x 1.0 x 1.0 cm)

Wt: 6.7 g

Piata Mine, Bahia, Brazil

A single tetragonal prismatic Xenotime crystal makes up this small specimen. It has very little damage and shows very good but slightly interrupted form, but its edges are still well-defined and its faces are smooth and possess a vitreous luster. Like most Xenotimes from this locality, it has a moderately dark brown coloration with golden highlights and is translucent to dimly transparent along its edges. However, it does show transparence just beneath its surface, as rutile needles can be seen in all of the prism faces. Like most of our Xenotime specimens, there is no host rock present.

xen-5 ($105.00)

Piata Mine, Bahia, Brazil

XENOTIME specimen xen-6
$ 30.00

Dims: 0.5 x 0.2 x 0.2" (1.3 x 0.5 x 0.5 cm)

Wt: 10.0 g w/ specimen box

Novo Horizonte, Bahia, Brazil

A "parallel association" of at least 3 intergrown Xenotime prisms makes up this small thumbnail specimen. They do not exceed 0.5" (1.3 cm) in length or 0.1" (3 mm) in diameter, and only one appears to be damaged. They have excellent tetragonal form and one is doubly-termionated. They have the classic brown coloration with golden highlights and a bright pearly luster, and are only dimly translucent at best. There is no host rock of any sort present.

xen-6 ($ 30.00)

Novo Horizonte, Bahia, Brazil

XENOTIME specimen xen-7
$ 48.00

Dims: 0.7 x 0.2 x 0.1" (1.8 x 0.5 x 0.3 cm)

Wt: 10.3 g w/ specimen box

Novo Horizonte, Bahia, Brazil

This single Xenotime crystal is in very good condition, showing only a small amount of visible damage, and has good tetragonal prismatic form, with a steep 4-sided pyramidal termination. It has the standard brown color with golden highlights of material from this locality, and is only dimly translucent at best. There is no host rock attached to it, and it is affixed inside a plastic specimen box with an adhesive putty.

xen-7 ($ 48.00)

Novo Horizonte, Bahia, Brazil

XENOTIME specimen xen-8
$ 28.00

Dims: 0.6 x 0.3 x 0.2" (1.5 x 0.8 x 0.5 cm)

Wt: 10.1 g w/ specimen box

Novo Horizonte, Bahia, Brazil

This small thumbnail specimen consists of a "parallel association" of several heavily intergrown Xenotime crystals. These crystals are in excellent condition, showing almost no damage, and have excellent tetragonal prismatic form, even considering their intergrowth. All have well-defined edges and clean faces that possess a bright, nearly vitreous luster. They have the classic brown color with golden highlights, and are actually transparent and dimly clear! There is no host rock present. The piece is affixed to the inside of a cubic plastic specimen box with an adhesive putty.

xen-8 ($ 28.00)

Novo Horizonte, Bahia, Brazil

XENOTIME specimen xen-9
$ 85.00

Dims: 0.6 x 0.2 x 0.2" (1.5 x 0.5 x 0.5 cm)

Wt: 11.7 g w/ specimen box

Piata, Bahia, Brazil

A single Xenotime crystal comprises this thumbnail specimen. It may have started out as 3 separate crystals that grew together, but it is now effectively a single unit. The crystal is in excellent condition, showing very little damage, and has excellent tetragonal prismatic form, with well-defined edges and clean faces. It has the standard dark brown color with golden highlights of its species and a pearly luster, and is dimly translucent. There is no host or base rock attached to it, and the crystal is affixed inside a plastic specimen box with an adhesive putty.

xen-9 ($ 85.00)

Piata, Bahia, Brazil

XENOTIME specimen xen-10
$ 110.00

Dims: 0.9 x 0.3 x 0.2" (2.3 x 0.8 x 0.5 cm)

Wt: 13.2 g w/ specimen box

Novo Horizonte, Bahia, Brazil

This small thumbnail specimen consists of a single, well-formed Xenotime prism that is in excellent condition, showing little damage. It appears to consist of two very heavily intergrown crystals, but is essentially a single unit. Even with its intergrowth, its tetragonal prismatic form is excellent, with well-defined edges, clean faces and a steep pyramidal termination. It has the classic brown color with golden highlights of crystals from this locality and is moderately translucent. There is no host rock present, and it is affixed inside a plastic specimen box with a removable putty.

xen-10 ($110.00)

Novo Horizonte, Bahia, Brazil

XENOTIME specimen xen-11
$ 108.00

Dims: 0.8 x 0.3 x 0.2" (2.1 x 0.7 x 0.6 cm)

Wt: 2 g

Piata, Bahia, Brazil

This small thumbnail specimen consists of a single, loose Xenotime crystal. The crystal is in very good condition, showing no damage apart from that at its base, and has a moderately good tetragonal prismatic form- it would appear that a few crystals grew into each other to form this one, and a few growth interruptions make it incomplete. Its brown color, golden-brown highlights and pearly luster are standard for its species, and it is translucent but shows noticeable transparence in some areas. The crystal is affixed inside a plastic specimen box with a removable putty.

xen-11 ($108.00)

Piata, Bahia, Brazil

XENOTIME specimen xen-12
$ 45.00

Dims: 0.5 x 0.4 x 0.3" (1.3 x 1.0 x 0.7 cm)

Wt: 12 g w/ specimen box

Ibitiara, Bahia, Brazil

A single, incomplete Xenotime crystal comprises this small thumbnail specimen. It is in fair to poor condition, as its termination was broken off and slightly healed over before it was mined. Where intact, it has good tetragonal prismatic form. Its color is the standard dark brown with golden highlights, and its luster is pearly. The crystal is hot-glued into a plastic thumbnail box.

xen-12 ($ 45.00)

Ibitiara, Bahia, Brazil

XENOTIME specimen xen-14
$ 45.00

Dims: 0.9 x 0.4 x 0.4" (2.2 x 1.1 x 1.0 cm)

Wt: 7 g

Ibitiara, Bahia, Brazil

A single Xenotime crystal comprises this thumbnail specimen. The crystal is in very good condition, showing only a small amount of damage at one end, and has moderately good tetragonal prismatic form- it shows some evidence of double-termination. Its brown color with golden highlights and pearly luster are standard for the specie, and it is translucent and appears to contain some rutile needles. There is no host rock present, and the piece is affixed inside a thumbnail box with a removable putty.

xen-14 ($ 45.00)

Ibitiara, Bahia, Brazil

XENOTIME specimen xen-13
$ 45.00

Dims: 0.8 x 0.3 x 0.2" (2.1 x 0.7 x 0.6 cm)

Wt: 4 g w/ foam base

Ibitiara, Bahia, Brazil

A single Xenotime crystal comprises this thumbnail specimen. It is in excellent condition, showing no fresh damage, and has a reasonably good tetragonal prismatic form that is interrupted by many intersecting rutile needles. The Xenotime has the standard brown color with golden highlights and a pearly luster, and is only translucent. All of the intersecting rutiles are broken and incomplete, and have the golden color and nearly metallic luster that are standard for their specie. The piece is affixed inside a plastic specimen box with an adhesive putty.

xen-13 ($ 45.00)

Ibitiara, Bahia, Brazil