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The chemical formula of mineral Arfvedsonite is indicated by the formula Na3(Fe,Mg)4FeSi8O22(OH)2 or Sodium Iron Magnesium Silicate Hydroxide. Arfvedsonite is actually a Silicate mineral. Mineral Arfvedsonite was named after Johan August Arfvedson (1792-1841), a Swedish chemist. It was first discovered in the year 1923 at Greenland province. Arfvedsonite is known to crystallize in 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. Arfvedsonite is also a member of the Amphibole Group, a group comprising important rock-forming minerals. Arfvedsonite is a sodium-rich mineral. This is considered as one of the rare member of the Amphibole Group. Nepheline syenites and Agpaitic pegmatites are considered as actual treasures troves of rare minerals. When specimens are found hosted by them, these specimens surely would appear in any good rock shop. Arfvedsonite mineral is considered as a wonderful accessory mineral to the many exotic and rare mineral species.

 

            In the field of optical mineralogy, it has been chemically known that mineral Arfvedsonite actually belongs to the solid solution series. In optical mineralogy, a series where two or more elements exist with the ability to substitute one another without changing the chemical structure of the mineral is called a solid solution series. Each mineral acting as the end member of the series is distinct from one another. In this case under discussion, the series involves the ferrous iron and magnesium ions. The iron-rich member is called the Arfvedsonite. The other member that is magnesium-rich is called magnesio-arfvedsonite. These two minerals can be easily distinguished from one another by any ordinary means. Arfvedsonite is often found in association with other sodic phases such as aegirine-augite and aenigmatite.

 

            Arfvedsonite is most commonly found in greenish-black color and could actually appear more splendidly wonderful when specimen is viewed in transmitted light of polarized light microscope used in the field of optical mineralogy. Mineral Arfvedsonite may also appear dark gray or black when viewed under petrographic polarizing microscopes for mineralogists. The hardness of mineral Arfvedsonite when it is evaluated using the Mohs scale method is commonly found ranging from 5.5 to 6.0. Arfvedsonite is most commonly found exhibiting perfect cleavage in two directions at about 56-degree and 124-degree angles that could actually appear more clearly visible when mineral specimen is closely evaluated in plane light of polarizing light microscope used in the field of optical mineralogy. Arfvedsonite is commonly found leaving a dark bluish-gray streak when mineral is rubbed on a white porcelain streak plate. Arfvedsonite mineral is most commonly fund showing uneven to subconchoidal fracture when specimen is closely evaluated under several adjustments on the aperture diaphragm of petrographic polarizing microscope used in optical mineralogy. The specific gravity measure is commonly found ranging from approximately 3.1 grams per cubic centimeters to 3.4 grams per cubic centimeters. But typically it is about 3.4 grams per cubic centimeters, which is considered slightly above average for non-metallic minerals.

 

            Arfvedsonite crystals are most commonly found translucent and sometimes opaque in appearance. The crystal habit of mineral Arfvedsonite as described in the field of optical mineralogy usually includes blocky prismatic to acicular crystal that are usually splendidly exhibited when viewed in transmitted light of polarizing microscope for mineralogists. Sometimes Arfvedsonite crystals may also be found in tabular form in radial stellate aggregates that can be seen more splendidly exhibited when viewed with the aid of petrographic polarizing light microscope used in optical mineralogy. There are some specimens appearing up to 20cm in length. Arfvedsonite minerals may also appear in fibrous formations, which can be found exhibiting nice and wonderful microscope views under polarizing microscopes used in the field of optical mineralogy. Some other massive and sometimes lamellar are also found exhibited under transmitted and reflected light of polarized light microscope for mineralogists. They can be also found twinned when evaluated between crossed nicols of petrographic polarizing microscope for mineralogists. Lamellar twinning can be clearly found when viewed with the aid of petrographic polarizing microscopes. Arfvedsonite shows high surface relief when examined under several adjustments on the aperture diaphragm of the polarizing light microscopes. Longitudinal extinction angles are commonly found when the mineral is evaluated between crossed nicols of polarized microscopes. In some sections, there are extinctions found symmetrical to the outlines or the cleavage traces when viewed between crossed nicols of polarizing light microscopes.

 

Arfvedsonite usually shows vitreous luster when specimen is closely evaluated in reflected light of petrographic polarizing microscope used in the field of optical mineralogy. Arfvedsonite may also show silky luster if they appear in fibrous form when examined in reflected light of polarized microscope for mineralogists. Mineral Arfvedsonite is most commonly found showing biaxial negative figure closely evaluated between crossed nicols of petrographic polarizing light microscopes used in optical mineralogy. Arfvedsonite mineral is commonly found weakly pleochroic when viewed in plane-polarized light of polarized microscopes for mineralogists. Arfvedsonite is usually found displaying polarization colors from dark-green to blue-green to brownish-green under polarized microscopes used in optical mineralogy. Arfvedsonite crystals may show lengthwise striations in both reflected and transmitted light of polarized microscopes. The index of refraction found when the mineral is evaluated in plane-polarized light of petrographic polarizing microscope is commonly is 1.69. Arfvedsonite commonly shows low birefringence and exhibiting interference colors that usually masked by color of the mineral. Interference colors are found in mid to upper second order when examined between crossed nicols of petrographic polarizing microscope. It shows relatively strong dispersion when viewed under polarized microscope used in optical mineralogy.

 

            Arfvedsonite mineral is most commonly found associated with other minerals like aegirine, nepheline, makatite, serandite, and many others. Also associated with several feldspathoids and various feldspars and micas. Arfvedsonite minerals are rather rare and usually occur in alkalic igneous mineral occurring in colored sodium-rich nepheline syenite intrusions. They can be also found in agpaitic pegmatites, which are considered having little existence around the world. They are commonly constituted in silica-saturated felsic rocks of the midalkaline and alkaline series. Arfvedsonite commonly occur in type of localities like Mont Saint-Hilaire, Quebec, Canada. It can be also found in the Ilimaussaq Intrusion at Southern Greenland. Several occurrences may be also found at the agpaitic pegmatites of the Kola Peninsula, Russia. There is also some reported occurrence in Langesundfjord, Norway.



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Tuesday, March 31st, 2009 at 7:56 am
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The Silicates Mineral Class
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