Description
The mineral bastnäsite is a fluorine-containing lanthanum-cerium-yttrium carbonate with the chemical formula (La,Ce,Y)CO3F. Transparent to translucent yellow to reddish-brown bastnäsite has a vitreous to oily luster, a white streak color, and the mineral's cleavage is imperfect according to the crystal plane [1011] and indistinct according to [0001]. The crystal system is hexagonal. Bastnäsite has an average density of 4.97, a hardness of 4 to 5, and is not to weakly radioactive. Depending on the exact composition, the gamma ray value, according to the American Petroleum Institute, ranges from 0 (for the Y-containing variety) to 60,386.61 for the cerium-containing variety. The refractive index is 1.717 to 1.818, and the birefringence is 0.1010. The mineral bastnäsite is named after the Bastnäs mine in Sweden, where it was first discovered. Bastnäsite is a mineral that forms in the weathering zones of alkaline igneous rocks. The type locality of bastnäsite is the Bastnäs mine in Riddarhyttan County, Västermanland, Sweden. Bastnäsite is an important ore mineral for the Rare Earth Elements.
