Polycrase-(Y)
Current inventory:  0 gems
 

  
Polycrase is named from the Greek for many and a mixture, in reference to the large number of chemical elements contained.

Discovery in 1870;   IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Y,Ca,Ce,U,Th)(Ti,Nb,Ta)₂O₆

Yttrium Calcium Cerium Thorium Niobium Tantalum Oxide

Molecular Weight:

372.96 gm

Composition:

Calcium

1.07 %

Ca

1.50 %

CaO

Cerium

3.76 %

Ce

4.40 %

Ce₂O₃

Yttrium

11.92 %

Y

15.14 %

Y₂O

Thorium

6.22 %

Th

7.08 %

ThO₂

Uranium

6.38 %

U

7.67 %

UO₃

Tantalum

14.56 %

Ta

17.77 %

Ta₂O₅

Titanium

15.41 %

Ti

25.70 %

TiO₂

Niobium

14.95 %

Nb

21.38 %

Nb₂O₅

Oxygen

25.74 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.19-10

Nickel-Strunz 10th Ed. ID:

4.DG.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
G : With large (+- medium-sized) cations; chains of edge-sharing octahedra

Related to:

Polycrase Group. The Yttrium-dominant analogue of Uranopolycrase.

Varieties:

None

Synonyms:

Polycrase, Polycrasite

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal; commonly Metamict (Amorphous)

Crystal Habit:

Crystals are stout prismatic || [001], typically flattened on {010}, may be striated || [001] by twinning, to 5 cm; commonly in parallel to radiating aggregates; massive.

Twinning:

Common on {201}; rare on {101} or {013}

Physical Properties

Cleavage:

None

Fracture:

Conchoidal to Subconchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.5

Density:

4.70 - 5.90 (g/cm³); may be less when altered

Luminescence:

None

Radioactivity:

Strong; GRapi = 603,860.75 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Black, Brownish Black, Greenish Black; Brown to Yellow-Brown in transmitted light

Transparency:

Opaque, transparent in thin fragments

Luster:

Brilliant Submetallic, Waxy to Resinous on fractures

Refractive Index:

2.250  Isotropic

Birefringence:

0.00  (Isotropic)

Dispersion:

n/a

Pleochroism:

None

Occurances

Geological Setting:

In granite pegmatites; rarely as a detrital mineral.

Common Associations:

Gadolinite, Columbite, Xenotime, Monazite, Allanite, Zircon, Garnet, Beryl, Magnetite, Fluorite

Common Impurities:

Ca, Ce, U, Th, Ta

Type Locality:

Rasvåg feldspar quarries, Hidra (Hitterø), Flekkefjord, Vest-Agder, Norway

Year Discovered:

1870

View mineral photos:

Polycrase-(Y) Mineral Photos and Locations

More Information

Mindat.org 
Webmineral.com

Polycrase-(Y) is a very rare radioactive mineral that belongs to the Polycrase Group of minerals that includes Euxenite-(Y), Polycrase-(Y) and Yttrocrasite-(Y). Because of the rare earth metals in its structure, Polycrase-(Y) is one of several minerals called "Rare Earth Oxides". Other rare earth oxides such as Aeschynite, Fergusonite and Samarskite have very similar properties to Polycrase-(Y) and are often associated with each other. Faceted Polycrase-(Y) gems are extremely rare and really only faceted as a collector's oddity. Polycrase-(Y) is a strongly radioactive mineral and should be stored away from other gems and minerals that are subject to damage from radioactivity and of course human exposure should be limited!

Less common than euxenite. Some localities for well-characterized material include: from Rasvåg, Hidra (Hitterö) Island, near Flekkefjord, and many other places in Norway. At Slättåkra, Län Jönköping, Sweden. In Lyndoch Township, and about eight km south of Maberly, Ontario, Canada. In the USA, from Zirconia, Henderson County, North Carolina; at Marietta, Greenville County, South Carolina; in the Overlook quarry, Day, Saratoga County, New York; from the Trout Creek Pass pegmatite district, in Park County, east of Buena Vista, Colorado; at the Baringer Hill pegmatite, 26 km west of Burnet, Llano County, Texas. From Santa Clara, near Tocantins, Minas Gerais, Brazil. At Cooglegong, Western Australia. Probably from many places in Madagascar but analyses are lacking for the distinction from abundant euxenite.
 

  
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