Allactite
Encyclopedia
Allactite is a rare arsenate mineral
Arsenate mineral
Arsenate minerals usually refer to the naturally occurring orthoarsenates, possessing the 3- anion group and, more rarely, other arsenates with anions like AsO32- or [AsO22]- . Arsenite minerals are much less common...

 of metamorphosed
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...

 manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 ore deposits. It is found in Sweden and New Jersey, USA. Its name originated from Greek αλλάκτειν (allaktein) meaning "to change", referring to the strong pleochroism
Pleochroism
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...

of the mineral.
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