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The chemical formula of Celestite is indicated by SrSO4. Celestite is a Sulfate mineral. This mineral is known to crystallize in the orthorhombic system. In optical mineralogy, the orthorhombic crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. When viewed under petrographic polarizing light microscope, mineral Celestite is known to have biaxial positive figure. The indices of refraction of Celestite vary from 1.621 to 1.632. The birefringence of the mineral is from 0.009 to 0.010. When evaluated with the aid of the petrographic polarizing microscope, mineral Celestite is commonly found having optical angle of about 51 degree. When viewed closely under polarized microscope used in optical mineralogy, Celestite commonly displays a moderate positive relief.

 

            The hardness measure of the mineral Celestite when it is evaluated using the Mohs scale method is usually 3. The specific gravity measure of Celestite is usually 3.97 grams per cubic centimeters. Celestite is commonly found colorless, white, or pale blue in hand sample. It is less commonly found reddish, greenish, or brownish in color. When rubbed on a white porcelain streak plate, Celestite is commonly found leaving a white streak. When viewed in reflected light of petrographic polarizing microscope, Celestite is commonly found exhibiting a vitreous luster.

 

            Celestite is commonly found colorless in thin section or grain mount. Large grains of colored Celestite mineral samples that display pale colors usually exhibit a weak pleochroism. Pleochroism of these samples is usually found in shades of lavender, blue, violet, or blue green. Mineral Celestite commonly appears in a variety of crystal habit. But the most common form is either tabular or elongate along the a axis. The crystals are less commonly elongate along the b or c axis. Celestite crystals also occur cleavable, granular, fibrous, or earthy masses.

 

            Mineral Celestite is commonly found having four cleavage directions. The most prominent cleavage is the single perfect cleavage in one direction. Another two good prismatic cleavage can be found intersecting at 75 degree and another poor single cleavage found in another direction. The cleavages can be seen more clearly visible when the sample is evaluated with the aid of the polarizing microscope used in optical mineralogy. Celestite minerals are rarely twinned.

 

            The indices of refraction of mineral Celestite when evaluated under petrographic polarizing microscope display relatively little variation. The interference colors seen in thin section are usually first-order gray and white when the samples are examined closely with the aid of the polarized microscopes used in optical mineralogy. These interference colors are sometimes found with a slight tinge of yellow. Some sections cut yield centered acute bisectrix figure with optical angle at about 51 degree. The optic axis dispersion of the sample when viewed under polarizing microscope is usually weak. There are some sections that show parallel extinction and low birefringence when closely evaluated with the aid of the petrographic polarizing microscope. With close examination, it can be found that the cleavage fragments, which lie on the dominant cleavage yield centered obtuse bisectrix figures.

 

            It has been studied in the field of optical mineralogy that Celestite may alter to Strontianite. It may be replaced by calcite, quartz, barite, sulfur, Witherite, or sometimes speudomorphically. Celestite can be easily distinguished despite the fact that it is most easily confused with gypsum or barite. When compared to Barite, Celestite has lower indices, with slightly lower birefringence and larger optic angle. Gypsum on the other hand has inclined extinction. Mineral Celestite is usually found in sedimentary rocks. It can be also possibly found in hydrothermal vein deposits.



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Wednesday, May 28th, 2008 at 4:57 am
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The Sulfates Mineral Class
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