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The chemical composition of mineral Johninnesite is indicated by the formula Na2Mg4Mn++12(AsO4)2(Si12O35)(OH)6. Johninnesite is also found in low temperature hydrothermal veins cutting metamophosed Fe-Mn ores. Mineral Johninnesite is commonly found from its type of locality at Kombat mine, located 37 km east of Otavi and 49 km south of Tsumeb in the north-central part of Namibia. Johninnesite was named for John Innes, mineralogist of the Tsumeb Corporation, for his contributions to the mineralogy of the Tsumeb and Kombat mines. Johninnesite is known to crystallize in the triclinic system of crystal formation. In optical mineralogy, this triclinic crystal system commonly comprises crystals having three axes, of which all are unequal in length and are positioned oblique to one another. Mineral Johninnesite is commonly found with good cleavage in one direction and poor in the other, all of which are found more clearly visiblw when evaluated closely with the aid of petrographic polarizing microscope used in the field of optical mineralogy. This mineral Johninnesite is commonly found yellow brown color in hand sample. The density measure of mineral Johninnesite is commonly found 3.48 grams per cubic centimeters. Most crystals of mineral Johninnesite are found transparent in appearance. It is also found showing conchoidal to uneven fracture. Uneven fracture is usually producing small, conchoidal fragments. Mineral Johninnesite is also found fibrous in form. This is forming crystals made up of fibers. It can be also found forming plumose or “mica-like” minerals forming aggregates of plume-like forms. This mineral Johninnesite can be also found in radial form where crystals radiate from a center without producing stellar forms similar stibnite. The hardness measure of mineral Johninnesite is usually ranging from 5 to 6. This mineral is also found with vitreous or glassy luster when evaluated in reflected light of polarized microscope used in the field of optical mineralogy. Johninnesite is also found leaving brownish yellow streak when rubbed on white porcelain streak plate. Johninnesite is also found to have biaxial negative figure with 0.0257 birefringence when it is evaluated between crossed nicols of polarized microscopes for mineralogists. It is also found showing distinct dispersion. Johninnesite is also found not radioactive.



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Friday, October 14th, 2011 at 5:19 am
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Optical Mineralogy
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