Polycrase

Polycrase is a rare mineral species belonging to the euxenite group, which are complex oxides with the general formula (Y,U,Ca,Th)(Nb,Ta,Ti)2O6. Polycrase itself is characterized by the presence of yttrium and uranium as the dominant rare earth and actinide elements, respectively, along with niobium and tantalum as the primary metallic constituents. It is often found as small, prismatic or stubby crystals, typically dark brown to black in color. The mineral is known for its strong radioactivity due to the presence of uranium and thorium.

Polycrase is found in a variety of geological settings, commonly associated with pegmatites, granitic intrusions, and metamorphic rocks. Notable occurrences have been reported in Scandinavia, particularly in Norway, as well as in North America. Due to its rarity and often fine-grained nature, polycrase is not a commercially significant source of rare earth elements, although it is of scientific interest for mineralogical studies and understanding the behavior of radioactive elements in geological formations. Its chemical composition can vary significantly, leading to the identification of various subspecies or varieties based on the relative proportions of the constituent elements.