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The chemical formula of mineral Cummingtonite is indicated by (Mg, Fe)7Si8O22(OH)2 or Magnesium Iron Silicate Hydroxide. Cummingtonite is actually a Silicate mineral. The name Cummingtonite was derived from the name of its type of locality in Cummington, Massachusetts in the United States. The first mineral specimen of Cummingtonite was actually found in this type of locality in the year 1824. Mineral Cummingtonite is known to crystallize in the monoclinic system of crystal formation. In 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.

 

Mineral Cummingtonite is most commonly used as a mineral specimen and it is often found exhibiting fascinating microscope appearance when evaluated with the aid of petrographic polarizing light microscopes used in optical mineralogy. Cummingtonite is also limited to some asbestos uses. One form of this Cummingtonite mineral is the variety called Amosite. This Cummingtonite variety is in asbestos form and can be actually used as asbestos, which has many industrial uses. Different minerals with interesting fibrous habit when viewed with the aid of polarizing light microscopes most commonly form asbestos. And this asbestos has many uses in industry despite some health risk. Cummingtonite asbestos is being mined in South Africa for its own specific use. Cummingtonite mineral is a known member of the Cummingtonite-Grunerite solid solution series where it is considered as the middle member.

 

            Mineral Cummingtonite is found sharing the same chemistry with another interesting mineral called anthophyllite. Mineral Cummingtonite and anthophyllite are actually polymorph minerals. In optical mineralogy, polymorph minerals means that the minerals have the same chemistry but with different structures. Anthophyllite is known to crystallize in the orthorhombic system while Cummingtonite is monoclinic. With regards to their physical color appearance, they both have the same distinctive brown color that is usually clearly exhibited under geological polarizing light microscopes. The two minerals are usually hard to differentiate from each other although mineral Cummingtonite is slightly denser and most often found having typically darker shade. And without the optical or X-ray test, Cummingtonite and anthophyllite minerals are indistinguishable from other amphibole minerals.

 

            Mineral Cummingtonite is commonly found in dark grayish or greenish-brown and dark green color that could appear more interesting when viewed under polarizing light microscope used in optical mineralogy. Cummingtonite is also most commonly found showing silky to vitreous luster that is commonly found more clearly exhibited when the mineral is viewed in reflected light of polarizing microscope for mineralogists. The cleavage found displayed by Cummingtonite is usually good in two directions at about 56-degree to 124-degree angles when it is evaluated with the aid of petrographic polarizing microscopes for mineralogists. Cummingtonite also exhibits splintery fracture when the mineral is evaluated under several adjustments on the aperture diaphragm of the petrographic polarizing microscope used in optical mineralogy. There can be also a brittle conchoidal fracture that can be found when the mineral is evaluated with the aid of geological polarizing light microscopes. A very brittle fracture producing small conchoidal fragments can be seen clearly visible when the mineral is evaluated in plane light of polarizing light microscopes for geologists. The specific gravity measure of the mineral usually gives an approximate value ranging from 3.1 grams per cubic centimeters to 3.6 grams per cubic centimeters, which is commonly considered average to slightly above average. The hardness measure of the mineral when it is evaluated using the Mohs scale method is commonly found ranging from 5 to 6. Cummingtonite is most commonly found leaving a white streak when mineral specimen is rubbed on a white porcelain streak plate.

 

            Most Cummingtonite mineral crystals are found transparent to opaque in appearance. The crystal habit of Cummingtonite as described in optical mineralogy usually includes fibrous formation that exhibits wonderful microscope views under polarized microscopes. Cummingtonite can be also found in lamellar and radiating masses that are commonly very interesting and are splendidly and wonderfully exhibited when viewed with the aid of polarizing light microscopes. Cummingtonite mineral crystals are sometimes found as stalky aggregates that are usually interesting when viewed under polarized light microscopes for mineralogists. Sometimes mineral Cummingtonite is found forming interesting crystal columns when viewed under petrographic polarizing microscopes used in optical mineralogy. But generally, Cummingtonite mineral crystals are found as anhedral to subhedral crystals in matrix. Twinned Cummingtonite crystals are also common and they are usually found visible when viewed with the aid of petrographic polarizing light microscopes for mineralogists. The type of twinning found is usually simple and sometimes lamellar, which is commonly clearly exhibited when viewed under petrographic polarizing light microscopes.

 

            Cummingtonite is most commonly found having moderate surface relief when the mineral is evaluated under some minor adjustments on the aperture diaphragm of polarizing microscope used in optical mineralogy. Cummingtonite is most commonly found showing biaxial positive figure when evaluated between crossed nicols of petrographic polarizing light microscopes. The birefringence found exhibited by mineral Cummingtonite in plane-polarized light of polarizing microscopes for mineralogists is usually ranging from 0.0250 to 0.0370. Mineral Cummingtonite is commonly found exhibiting polarization colors comprising colorless, pale greenish yellow or pale violet shades when mineral section is evaluated between crossed nicols of petrographic polarized microscopes used in optical mineralogy. Mineral Cummingtonite is also not fluorescent when exposed to ultra violet light. The refractive indices of mineral Cummingtonite are usually found ranging from 1.639 to 1.708 when the mineral is viewed in plane-polarized light of petrographic polarizing microscope for mineralogists. There is no specific data found on the toxicity and health danger for mineral Cummingtonite. However, the specimens of this mineral should be treated with great care and use of sensible precautions upon handling them is recommended. Mineral Cummingtonite is not a radioactive mineral.

 

Cummingtonite is commonly found associated with actinolite, anthophyllite, hematite and hornblende. The best field indicators of the mineral Cummingtonite usually include fracture, hardness, color, crystal habit, cleavage and density. Mineral Cummingtonite is commonly found in contact and regional metamorphic rocks. It is most commonly found in the metamorphosed magnesium-rich rocks and occurs in amphibolites. Mineral Cummingtonite can be also found in dacites and some other felsic igneous rocks. Cummingtonite mineral notably occurs at Cummington, Hampshire County, Massachusetts, South Africa, Scotland, Sweden, La Paz County in Arizona and the Homestake Gold Mine in Lawrence County, South Dakota, USA.



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Thursday, January 29th, 2009 at 4:06 am
Category:
The Silicates Mineral Class
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