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The chemical formula of mineral Cancrinite is indicated by Na6Ca2Al6Si6O24(CO3)2 or Sodium Calcium Aluminum Silicate Carbonate. Cancrinite is actually a Silicate mineral. Cancrinite was originally found at the Ural Mountains in Russia in the year 1839. It was actually named after Count Egor Frantsevich Kankrin or Georg von Cancrin (1774-1845), a Russian minister of finance. Cancrinite is known to crystallize in the hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes.

 

            Cancrinite minerals are also known members of the feldspathoid group of minerals although considerably rare in occurrence. The feldspathoids are those minerals with chemical composition that are close to the chemistries of the alkali feldspars but with poor silica or SiO2 content. Cancrinite minerals are commonly used as mineral specimens. They are commonly found exhibiting a nice and splendid microscope views under polarized light microscopes. Cancrinite minerals can effervescence in warm hydrochloric acid. The liberation of the carbon dioxide gas, which forms the bubbles, is due to the reaction of the hydrochloric acid with the carbonate ion. The effervescence displayed by the mineral is very diagnostic to Cancrinite since no other silicates can do this. But effervescence is actually very common in the carbonates minerals.

 

            Cancrinite is most commonly found in shades of yellow, orange, pink, white or blue when viewed in both reflected and transmitted light of geological polarizing microscopes used in optical mineralogy. Cancrinite is also commonly found exhibiting a vitreous or pearly luster in reflected light of petrographic polarizing microscope. When mineral specimen Cancrinite is evaluated between crossed nicols of polarizing light microscope for mineralogists, it is commonly found displaying a perfect prismatic cleavage in three directions but is usually rarely seen in massive specimens. Cancrinite also exhibits a conchoidal to uneven fracture when it is examined under several adjustments on the aperture diaphragm of the polarized microscope used in optical mineralogy. In the field of optical mineralogy, conchoidal fractures are commonly developed in brittle materials, which are characterized by smoothly curving surfaces. The specific gravity measure of mineral Cancrinite is commonly found ranging from 2.4 grams per cubic centimeters to 2.5 grams per cubic centimeters, which is considered average. The hardness measure of mineral Cancrinite when it is evaluated using the Mohs scale method is commonly found ranging from 5 to 6. Cancrinite is usually found leaving a white streak when mineral specimen is rubbed on a white streak plate.

 

            The crystal habit of mineral Cancrinite as described in optical mineralogy commonly includes massive or granular forms. Crystals in massive form are uniformly indistinguishable crystals forming large masses. Sometimes they can be also found having prismatic to columnar crystals. Prismatic crystals usually have their dominant faces as that of the prism. Prismatic crystals are usually shaped like slender prisms. Cancrinite will actually effervescence in warm hydrochloric acid. Cancrinite is most commonly found showing a uniaxial negative figure when it is viewed between crossed nicols of petrographic polarizing microscopes. The refractive indices of Cancrinite are usually found ranging from 1.507 to 1.503. Maximum birefringence is usually found in a range of 0.012 to 0.025. Cancrinite is most commonly found exhibiting a low surface relief when the mineral specimen is evaluated under polarizing light microscope for mineralogists. There is no specific data on the toxicity and health dangers for mineral Cancrinite. However, specimens of Cancrinite should be treated with great care and use of sensible precaution is advised upon handling them. Cancrinite are also not radioactive minerals.

 

Cancrinite, a feldspathoid mineral is almost exclusively found in intrusive or plutonic rocks. This is true despite the fact that feldspathoid minerals are known to be both extrusive and intrusive igneous rocks. The exclusiveness of Cancrinite in intrusive rocks is may be due to the tremendous pressures that is required to force the large carbonate ions into the structures of Cancrinite. Two other larger ions, the sulfate ions and the chlorine ions can be also contained at some percentage amount in the chemical structure of mineral Cancrinite. The feldspathoid minerals are actually similar to zeolites in terms of their wide-open structures, which commonly allow large ions to be incorporated into them.

 

            Cancrinite is most commonly found associated with several interesting minerals including the feldspars like biotite, sodalite, albite, nepheline, hornblende and several other feldspathoid minerals. The best field indicators of Cancrinite minerals commonly include locality, hardness, reaction to acids and its splendid association with several other wonderful minerals. Cancrinite mineral commonly occurs as an alteration product of nepheline and feldspar in the nepheline syenite and related rocks. It can be also found forming in the metamorphic rocks and also in contact zones between igneous intrusive rocks and limestones. Cancrinite has been also found in gneisses. It also occurs in contact metamorphic limestones. Cancrinite minerals notably occur at some types of localities including India, the Fen Region of Norway as well as the Kola Peninsula in Russia and the Iron Hill in Colorado, USA and also in Finland.



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Monday, December 29th, 2008 at 6:25 am
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The Silicates Mineral Class
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