Perite

Perite is a mineral that has a general chemical formula of PbBiO₂Cl. The name is given for Per Adolf Geijer, a Swedish economic geologist with the Geological Survey of Sweden, who discovered the mineral in 1960 outside of Langban, Sweden. Perite is orthorhombic, which means crystallographically, it contains three axes of two of equal length (the bases a and b) and one of a little longer or shorter length. All three bases intersect at a 90° angles. It belongs to the space group Cmcm {C2/m 2/c 21/m}. In terms of its optical properties, Perite is anisotropic which means the velocity of light varies depending on direction through the mineral (i.e. it is birefringent). Its calculated relief is 1.45-1.461, which is moderate. It is colorless in plane polarized light, and it is weakly pleochroic. Perite is found in areas near igneous extrusions in places like the Western United States, Southern Australia, and scattered around Europe.