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

uranium Uranium is a chemical element; it has chemical symbol, 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. Ura ...

yttrium Yttrium is a chemical element; it has Symbol (chemistry), 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 a ...

oxide mineral The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. Minerals with complex anion groups such as the sil ...

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 mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...

of 5 to 6 and a

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

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 conside ...

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

granitic A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

s. 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 Flekkefjord () is a List of municipalities of Norway, municipality in Agder county, Norway. It is located in the Traditional districts of Norway, traditional district of Lister Region, Lister. The administrative centre of the municipality is the ...

, 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