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Perite

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Perite
Perite, from Blue Bell Claim, San Bernardino County, California, United States of America
General
CategoryHalide mineral
Formula
(repeating unit)
PbBiO2Cl
Strunz classification3.DC.30
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupBmmb
Unit cella = 5.62 Å, b = 5.57 Å,
c = 12.42 Å; Z = 4
Identification
Formula mass483.63 g/mol
ColorYellow
Crystal habitPlatey crystals, pseudotetragonal
CleavageFair on {001}
Mohs scale hardness3
LusterAdamantine
StreakYellow
DiaphaneityTranslucent
Specific gravity8.16
Optical propertiesBiaxial (+)
Refractive indexncalculated2.29 - 2.3
PleochroismTrichroic
References[1][2][3][4][5]

Perite is a mineral that has a general chemical formula of PbBiO2Cl.[3] 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.[5] 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.

Crystallography

Perite belongs to the Orthorhombic crystal system, and has the properties of 2/m 2/m 2/m crystal class. Therefore, perite has 3 mirror planes and 3 twofold rotation axes.

References