if (document.getElementById != null) White, Gray, Bluish white, Reddish white, Greenish white. Our Recommended Book Selection at Amazon.com, Financial Donations and Collection Acquisitions. Actual formula of end Comments: Colorless, lustrous blocky albite crystals to 3 cm … { Massive - Granular - Common texture observed in granite and other igneous rock. The extinction angle is an optical characteristic and varies with the albite fraction (%Ab). Comments: Colorless, lustrous blocky albite crystals to 3 cm in size with a thick dusting of micaceous green micro chlorite. Rockhounds Discussion Group on Yahoo Groups Three varieties have gemstone uses: See the individual group members for localities. Scale: Picture size 3x3 cm. "); Link to . Scale: 47x30x7 mm. Albite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series.Albite is one end member, containing sodium and no calcium. From the Greek plagios - "oblique" and klao - "I cleave" in allusion to the obtuse cleavage angles of the good cleavages. else { if (headTags.length > 0) Location: Taquaral, Minas Gerais, Brazil. }, Jeff Weissman / Photographic Guide to Mineral Species, Minerals in Thin Section-University of North Carolina. Minerals in this series are a homogenous mixture of albite and anorthite. © Jeff Weissman / Photographic Guide to Mineral Species, Comments: Clear glassy crystalline oligoclase with milky quartz and muscovite. members are: We strive for accurate content and locality information. html += headTags[0].innerHTML; var headTags = document.getElementsByTagName("head"); The composition of plagioclase feldspar is typicallyindicated by the general anorthite (% An) or albite (% Ab) fraction and iseasily determined by measuring the refractive index or peel angle within thecrushed particles by measuring the refraction angle under a thin section. The color is due to optical interference on Bøggild exsolution lamellae. © Jeff Weissman / Photographic Guide to Mineral Species, Comments: Translucent andesine crystal twin. Original Rockhounds Discussion Group Feldspar - Feldspar - Chemical composition: All the rock-forming feldspars are aluminosilicate minerals with the general formula AT4O8 in which A = potassium, sodium, or calcium (Ca); and T = silicon (Si) and aluminum (Al), with a Si:Al ratio ranging from 3:1 to 1:1. Scale: See Photo. { (Na,Ca)Al1-2Si3-2O8. } if (printReadyElem != null) Additional images of each member mineral is indexed on the individual member pages. Plagioclase is the name of a group of feldspar minerals that form a solid solution series ranging from pure albite, Na(AlSi3O8), to pure anorthite, Ca(Al2Si2O8). There are several named plagioclase feldspars that fall between albite and anorthite in the series. NCalc= 1.56 - from Gladstone-Dale relationship (K, NAME( Duda&Rejl90) PHYS. alert("Sorry, the print ready feature is only available in modern browsers. { Español Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Ask-A-Mineralogist from the Mineralogical Society of America Common world wide occurrences. html += '\n\n\n'; © Dave Barthelmy, Comments: Rectangular cleavage fragment of salmon-orange oligoclase (sunstone) feldspar. The composition of a plagioclase feldspar is typically denoted by its overall fraction of anorthite (%An) or albite (%Ab), and readily determined by measuring the plagioclase crystal's refractive index in crushed grain mounts, or its extinction angle in thin section under a polarizing microscope. Chemical Composition: Ranges from NaAlSi 3 O 8 (Albite) to CaAl 2 Si 2 O 8 (Anorthite) Color: Typically white to gray, may also range from colorless, through shades of off-white, to yellowish, pink, reddish brown or nearly black. html += printReadyElem.innerHTML; Cleavage: One perfect cleavage and one good cleavage that meet at nearly 90° Hardness: 6 to 6.5 (harder than glass) Specific Gravity } printWin.document.close(); alert("Could not find the printReady section in the HTML"); Scale: 17 x 15 x 7.5 cm matrix. } Mindat.org's Discussion Groups The names of the minerals in the series are arbitrarily given based upon their relative abundance of albite and anorthite. The minerals of the plagioclase series are listed in the table below along with their relative abundance of albite (Ab) and anorthite (An). Location: Miyake-jima, Shizuoka, Japan. Scale: 7.4 x 5 cm. Ask about Plagioclase here : The exact composition of the various feldspar minerals depends on what elements balance the oxygen, which has two bonds to fill (remember H 2 O?).

plagioclase feldspar chemical formula

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