Marthozite
Encyclopedia
Marthozite is an orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...

 mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 that has a general formula of Cu(UO2)3(SeO3)3(OH)2·7H2O. It was named after French mineralogist Aime Marthoz, former Director-general of the Union Miniere du Haut Katanga
Union Minière du Haut Katanga
The Union Minière du Haut Katanga was a Belgian mining company, once operating in Katanga, in what is now the Democratic Republic of the Congo...

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It is usually found in cavities in selenian digenite
Digenite
Digenite is a copper sulfide mineral with formula: Cu9S5. Digenite is a black to dark blue opaque mineral that crystallizes with a trigonal - hexagonal scalenohedral structure. In habit it is usually massive, but does often show pseudo-cubic forms. It has poor to indistinct cleavage and a brittle...

. It is specifically found in the zones of oxidation of the Musonoi deposit in Katanga, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

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Marthozite is orthorhombic, meaning that it has three axes of unequal lengths all orthogonal to each other. Since it is orthorhombic, marthozite is biaxial, meaning that it has three different indices of refraction
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

. Marthozite is anisotropic, which means that it breaks light into one fast ray and one slow ray. Marthozite shows pleochroism from yellowish brown to greenish yellow.
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