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Click Here For Best Selection Of High Quality Polarizing Microscope

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The chemical formula of Anatase is given by TiO2 or Titanium Oxide. Anatase like Brookite is known as a polymorph of Rutile. However, Anatase is considered rare mineral, while Rutile is the most common one. Rutile, Brookite, and Anatase have different structures but they have the same chemical composition indicated by the formula TiO2. Their structures are consisting of TiO2 octahedra. Anatase at high temperature of about 915 degree Celsius, change to Rutile mineral structure. Anatase and Rutile have nearly the same properties except for their slight difference in crystal habit and cleavage. The difference between the two structures is in the manner in which edges of the octahedral are shared with neighboring octahedral. There are minor amounts of iron that may substitute for titanium and there are also some reported substitution of niobium or thalium. This distinction is brought about by their differences in structural formations. The term Anatase was derived from the Greek word anatasis, which means extension. This was on account of the mineral’s steeper pyramid that is exhibiting much longer crystal vertical axis compared to that of Rutile mineral.

 

            Specimens of Anatase are usually exhibiting splendid images when viewed under polarizing microscopes. They are also considered classics in the mineral world. Anatase is sometimes associated with the magnificent mineral quartz. Anatase is more popular because of its interesting characters like its good luster and well-formed crystals that are wonderfully exhibited under petrographic polarizing light microscopes. Anatase commonly appear in variations of colors from brown to black and sometimes may also exhibits hues of yellow and blue under reflected light of geological polarizing microscope. Anatase is actually yellowish brown, red brown, or black in hand samples. This mineral is less commonly found green, blue, gray, or colorless. Anatase exhibits an extremely positive relief when it is examined under several adjustments on the aperture diaphragm of polarizing light microscopes.

 

 Some transparent brown crystals of Anatase are occasionally cut for gem purposes. And this Anatase gem usually exhibits nice and splendid images when viewed with the aid of gemological microscopes. When viewed in reflected light of petrographic polarizing microscope, Anatase usually exhibits adamantine to submetallic luster. When rubbed on a white porcelain streak plate, Anatase leaves a colorless to pale yellow streak.

 

 A perfect basal cleavage in one direction at {001} and pyramidal in the other at {111} is very diagnostic of Anatase. All these cleavages are clearly visible when the mineral is evaluated under several adjustments on the aperture diaphragm of petrographic polarizing microscopes. Anatase is also weakly pleochroic when evaluated in plane light of polarizing microscopes. Mineral Anatase commonly show fragments in triangular form in cross section and this can be clearly seen when it is examined closely under  polarizing light microscopes for geologists. Crystals of mineral Anatase are usually elongated dipyramids. So the sections are usually rectangular or diamond-shaped. Mineral Anatase is also known to form anhedral grains.

 

 Twinning for Anatase crystals are generally not found even several adjustments on the polarizing microscope are made. But there can be possible occurrence on plane {112}. The fracture that is commonly exhibited by mineral Anatase under petrographic polarizing light microscope is conchoidal. The hardness measure for mineral Anatase when it is evaluated using the Mohs scale method is commonly ranging from 5.5 to 6.0. The specific gravity measure of mineral Anatase is approximately 3.90 grams per cubic centimeters.

 

Mineral Anatase is commonly found as small, isolated, and sharply developed crystals when viewed in polarizing microscopes. Crystal formations of mineral Anatase are distinct showing the eight-faced tetragonal dipyramids with sharp elongated points that are commonly found visible when viewed under geological polarizing light microscopes. This pronounced elongated points are the most common distinction of Anatase from octahedral crystals of other minerals. They may look like a stretched out octahedron when examined with the aid of petrographic polarizing light microscope. Anatase possesses tetragonal symmetry as mentioned and known to be similar to that of the Rutile mineral. The common pyramid of the mineral Anatase, when viewed under petrographic microscopes, has an angle over the polar edge of 82 degrees 9 minutes that is parallel to the faces of which there are perfect cleavages found. Crystals exhibits elongated dipyramids with rectangular or diamond-shaped sections that are splendidly exhibited under polarized microscopes. They may sometimes form anhedral grains. Two types of crystal habits are found exhibited by Anatase minerals under polarizing microscope for geologists. One is of simple acute double pyramids with an indigo-blue to black color showing steely luster. The other is of numerous pyramidal faces, usually flatter and sometimes of prismatic habit, exhibiting a variation of color from honey-yellow to brown.

 

The diamond-shaped cross section of mineral Anatase are fast parallel to the long diagonal. Depending on how the section is cut, the extinction of Anatase is usually found parallel, inclined, or sometimes symmetrical to {111} dipyramid faces and cleavage and also parallel to the basal cleavage at {001}. The indices of the mineral are usually found above the range of index of used oils. And when viewed under polarizing microscope, they commonly display extremely high relief in thin sections. The range of the indices of ordinary ray is about 2.55 to 2.60. A 0.07 birefringence found is very high. It actually produce creamy upper-order colors that often masked by the color of the mineral. The interference figure on the basal sections and fragments of mineral Anatase on {001} is commonly uniaxial negative. It is usually found with numerous isochromes that are often masked by the mineral color. Some dark colored varieties of Anatase may exhibit anomalously biaxial negative figure.

 

            Mineral Anatase may alter to rutile or may possibly be replaced by leucoxene. Leucoxene is an opaque amorphous titanium oxide that exhibits gray or white color in reflected light of petrographic polarizing light microscope. Anatase may resemble rutile but they could easily be distinguished from the other through their optic signs.mineral Brookite for instance, is another polymorph of mineral Rutile and they certainly have similar appearance. But then Brookite is found to be biaxial positive figure having indices ranging from 2.58 to 2.70. Mineral Anatase commonly occur as minor constituent of some igneous rocks such as granite and granite pegmatite as well as felsic volcanic rocks. They can be also occasionally found in hydrothermal vein deposits. They can be also found as detrial grains in some other clastic sediment because anatase is relatively stable in the weathering environment. It is also a common alteration product of other Titanium bearing minerals just like ilmenite or titanite. Transparent crystals of mineral Anatase can be found in Burke County, North Carolina as well as some localities like Germany, France, Brazil, Switzerland, and in Cornwall, England.



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Monday, March 24th, 2008 at 4:28 am
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The Oxides and Hydroxides Mineral Class
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