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The chemical formula of mineral Biotite is indicated by K(Fe,Mg)3AlSi3O10(F,OH)2 or Potassium Iron Magnesium Aluminum Silicate Hydroxide Fluoride. Biotite actually belongs to the Silicates mineral class. Biotite was named by J F L Hausmann in the year 1847. It was named in honor of Jean Baptiste Biot, a French physicist who discovered the optical properties of micas in the year 1816. Biotite minerals can be found in its characteristic crystal, which is the typical black brown color, which is clearly visible when the mineral is evaluated with the aid of a petrographic polarizing microscope used in the field of optical mineralogy. Just like other micas, the structure of Biotite mineral can be found as layered structure of iron magnesium aluminum silicate sheets, which are weakly bonded together by layers of potassium ions. These potassium ion layers commonly produce the perfect cleavage of the mineral. Although Biotite is rare considered as a valuable mineral specimen, it can actually compliment other minerals when they are found accompanied by Biotite. Large crystals of Biotite with hornblende and green apatite are found in Bancroft, Ontario, Canada.

 

            Biotite mineral specimens are commonly found in shades of brown and yellow, commonly with weathering, in transmitted light of polarizing microscope used in optical mineralogy. These minerals are usually found exhibiting a vitreous to pearly luster in reflected light of petrographic polarizing microscope for mineralogists. The cleavage found exhibited by Biotite when mineral specimen is evaluated between crossed nicols of polarizing light microscope used in the field of optical mineralogy is most commonly found perfect in one direction producing thin sheets or flakes. The fracture found is not readily observed even under several adjustments on the aperture diaphragm of polarized microscopes due to its cleavage. But the fracture is commonly found uneven. This usually shows flat surfaces that are commonly fractured in an uneven pattern. The hardness measure for Biotite mineral specimen is commonly 2.5. When Biotite mineral specimen is rubbed on a white streak plate, it usually leaves a white streak. The specific gravity measure of Biotite commonly gives an approximate value that is usually found in a range of 2.9 to 3.4 grams per cubic centimeters, which is considered slightly above average value.

 

            Biotite mineral crystals are known to crystallize in the monoclinic system of crystal formation. In the field of optical mineralogy, the monoclinic system of crystal formation comprises crystals having three axes of unequal lengths. Two of which are usually found in a position that is oblique or not perpendicular to one another. However, both of which are commonly found perpendicular to the third axis. The crystals of Biotite are commonly found transparent to translucent in appearance. Its crystal habit commonly includes tabular to prismatic crystals with a prominent pinacoid termination, which is clearly visible under a geological polarizing microscope used in the field of optical mineralogy. Tabular crystals are usually found in shapes like a book, when evaluated under petrographic polarizing microscope for mineralogists. The four prism faces of Biotite and two pinacoid faces usually form pseudohexagonal crystal plates. These crystals are actually showing a hexagonal outline when specimens are evaluated under polarizing microscopes used in optical mineralogy. Oftentimes, the sides of the crystal tend to tapper and can be possibly found having a look like a hard candy that has been sucked on. Biotite crystals can be also found as lamellar or granular rock forming masses, which is commonly providing the luster for most schists and gneiss. Biotite commonly shows thin laminae producing a lamellar structure. An impressive mineral specimen with considerable size can grow from a single large plate of Biotite crystal. Biotite crystals can be also found weathered as tiny aggregates, which are commonly exhibiting golden yellow with a nice sparkle that are usually producing a Gold of fools that has fooled many. Biotite minerals are commonly associated with feldspars, quartz, calcite, apatite, schorl, garnets and hornblende.

 

            Brown Biotite mineral commonly shows pleochroism under a petrographic polarizing microscope used in the field of optical mineralogy. When Biotite mineral specimen is viewed in a single polarizing filter. When the stage of polarizing microscope is rotated, a change in color of the grains can be seen from light brown to dark brown. Between crossed nicols of petrographic polarizing microscope, Biotite mineral specimen shows a high birefringence. Biotite commonly shows a moderate to moderately high surface relief under a polarized light microscope used in the field of optical mineralogy. These minerals are actually rarely twinned. The cleavage sheets of Biotite crystals are commonly found flexible and elastic. This means that they can be bent and will flex back to original shape. Biotite minerals are not really used extensively in the industry. It is commonly used to constrain the age of rocks and electrical devices. Biotite minerals are also used in fire extinguishers since they are fireproof. They are also ground up and added to other things such as paint, lubricant or greases and also as waterproofing sealers. Biotite forms a milky solution on boiling in strong acid. They are actually soluble in a strong sulfuric acid. They are also found slightly radioactive after several chemical evaluations. There is no specific data on the toxicity and health dangers for Biotite minerals. However, Biotite mineral specimens should be treated with great care and use of sensible precaution is advised upon handling them.

 

            Biotite mineral is considered as a common rock-forming mineral. It is commonly found present in at least some percentage in most igneous rocks and also in both regional and metamorphic rocks. They can be occasionally found in large sheets and more especially in pegmatite veins. Biotite is also an essential constituent of many metamorphic types of schist. It can also form in suitable compositions over a wide range of temperature and pressure. In the intermediate and felsic igneous rocks, Biotite mineral may be confused with amphibole. But Biotite has flat, slick, shiny faces that are broken by the numerous cleavages, which are typical to amphibole minerals. The best field indicators of mineral Biotite commonly include color, elastic sheets, crystal habit, cleavage and its splendid association with other interesting minerals. Biotite minerals notably occur at some types of localities that include Sicily, Russia, and many other localities around the world as well as Bancroft and Sudbury in Ontario, Canada.



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Friday, January 15th, 2010 at 4:38 am
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The Silicates Mineral Class
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