Polycrase or polycrase-(Y) is a black or brown metallic complex

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

yttrium Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a " rare-earth element". Yttrium is almost always found in co ...

oxide mineral with the chemical formula . It is amorphous. It has a

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by t ...

of 5 to 6 and a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

of 5. It is

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

due to its uranium content (around 6%). It occurs in

granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...

pegmatites. Polycrase forms a continuous series with the niobium rich rare earth oxide

euxenite Euxenite, or euxenite-(Y) (the official mineralogical name), is a brownish black mineral with a metallic luster. Chemistry It contains calcium, niobium, tantalum, cerium, titanium, yttrium, and typically uranium and thorium, with some other meta ...

. It was first described in 1870 at Rasvag, Hidra (Hittero) Island, near

Flekkefjord is a municipality in Agder county, Norway. It is located in the traditional district of Lister. The administrative centre of the municipality is the town of Flekkefjord. The villages of Sira, Gyland, Rasvåg, Kirkehavn, and Åna-Sira are ...

, Norway. It is found in Sweden, Norway, and the United States.

References

Mindat with location dataWebmineral
Uranium minerals Thorium minerals Calcium minerals Cerium minerals Yttrium minerals Lanthanide minerals Niobium minerals Tantalum minerals Titanium minerals Oxide minerals Amorphous solids Orthorhombic minerals Minerals in space group 60 Minerals described in 1870 {{oxide-mineral-stub