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The chemical formula of the mineral Jarosite is indicated by KFe3(SO4)2(OH)6 or Potassium Iron Sulfate Hydroxide. Jarosite is actually a Sulfate mineral. Jarosite is also a member of the Alunite Group of minerals. Mineral Jarosite was actually first described by August Breithaupt in 1852 from its type of locality at the Barranco del Jaroso in the Sierra Almagrera, Spain. Mineral Jarosite is known to crystallize in the trigonal system to which its structure can be seen clearly visible when evaluated with the aid of the polarizing microscopes for mineraogists.

 

Jarosite is commonly used as mineral specimen by mineralogists most especially in the field of optical mineralogy. It is often found exhibiting wonderful and interesting microscope images when viewed with the aid of the petrographic polarizing microscopes. Jarosite is a quite uncommon mineral species in the mineral world. It is actually closely related to another interesting mineral called natrojarosite. When viewed with the aid of the petrographic polarizing microscope, Jarosite is clearly found isostructural with mineral natrojarosite. In optical mineralogy, isostructural means the two minerals have the same crystal structure although they have different chemistries. The chemical composition of mineral Jarosite contains potassium instead of sodium in the formula of natrojarosite. The name of the mineral natrojarosite was derived from the Latin word natrium, which means sodium. Sodium also gets its symbol Na from this Latin word. In the absence of chemical tests, the two minerals are very difficult to distinguish.

           

            Mineral Jarosite is most commonly found exhibiting an amber yellow or brown color when viewed with the aid of petrographic polarizing light microscopes. Jarosite also most commonly found exhibiting a vitreous to resinous luster when viewed in reflected light of the polarized light microscope. Jarosite is commonly found having good cleavage in one direction but it can be only seen in larger crystals when evaluated with the aid of petrographic polarizing microscope used in optical mineralogy. Jarosite also exhibits uneven fracture when it is viewed with the aid of polarized microscopes used in optical mineralogy. The specific gravity measure of the mineral usually gives an approximate value ranging from 2.9 grams per cubic centimeters to 3.3 grams per cubic centimeters, which is considered average to slightly heavy for translucent minerals, but hard to obtain from crusts. The hardness measure of Jarosite when it is evaluated using the Mohs scale method is usually found ranging from 2.5 to 3.5. Jarosite is most commonly found leaving a pale yellow streak when rubbed on a white porcelain streak plate.

 

            Most Jarosite crystals are found transparent to translucent in appearance. The crystal habit of mineral Jarosite usually include tabular to flattened rhombohedral looking crystals that are most commonly found clearly exhibited when viewed with the aid of petrographic polarizing light microscopes for mineralogists. In optical mineralogy, the rhombohedron form is actually a combination of two trigonal pyramids that is more clearly visible when examined with the aid of polarized light microscopes for mineralogists. Jarosite crystals are somewhat scarce and small when found. Jarosite crystals are most commonly found in earthy masses, in films or crusts and sometimes in botryoidal and granular form.

 

            When viewed between crossed nicols of petrographic polarizing light microscopes, Jarosite is commonly found having uniaxial negative figure as also described in optical mineralogy. Jarosite mineral can be also found anomalously biaxial with a very small 2V and sectional development when evaluated under polarized light microscopes used in optical mineralogy. Mineral Jarosite commonly exhibits a high surface relief when it is examined under several adjustments on the aperture diaphragm of the polarizing microscope. The refractive index of the mineral Jarosite when it is evaluated with the aid of polarizing microscope is usually found ranging from 1.713 to 1.820. It also exhibits a visible pleochroism under petrographic polarizing microscopes. The maximum birefringence of mineral Jarosite under polarized light microscope is commonly ranging from 0.102 to 0.105. Mineral Jarosite is strongly pyroelectric. It is also insoluble to water but highly soluble in HCl. There is no specific data found on the toxicity and health dangers for mineral Jarosite. However, the specimens of this mineral species should be treated with great care and use of sensible precaution is advised upon handling them.

 

            Mineral Jarosite is commonly associated with other interesting minerals including turquoise, galena, barite, limonite, goethite, hematite and several other iron minerals. The best field indicators of mineral Jarosite usually include hardness, associations, color, and crystal habit. Jarosite is commonly found as secondary mineral in the oxidized zones of sulfide deposits. Mineral Jarosite notably occurs at several localities including Jaroso ravine, Sierra Almagrera, Spain and some areas in the United States such as Maricopa Co. in Arizona, the Iron Arrow Mine in Colorado as well as Idaho and California.



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Thursday, August 28th, 2008 at 3:22 am
Category:
The Sulfates Mineral Class
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