Shipping and handling. Sericite #2 thin section (hFOV 2mm) GET 360° LIVE INTERACTION. This item will ship to United States, but … It can be difficult to see cleavage in thin section due to orthoclase’s low relief. It had previously been recognized as a distinct species by J. J. Berzelius in 1824. Rhyolite Rhyolite: A collective term for silicic volcanic rocks consisting of phenocrysts of quartz and alkali feldspar, often with minor plagioclase and biotite, in a microcrystalline or glassy groundmass and having the chemical composition of granite. Usually found as micaceous flakes or tablets with irregular outlines, tabular parallel to {001}. Labradorite Na0:5¡0:3Ca0:5¡0:7Al1:5¡1:7Si2:5¡2:3O8 °c 2001 Mineral Data Publishing, version 1.2 Crystal Data: Triclinic. 00023. Plagioclase - NaAlSi 3 O 8--CaAl 2 Si 2 O 8 Plagioclase feldspars are the most common feldspar minerals because calcium is somewhat more common in the crust than potassium (3.6 and 2.8 percent of the crust, respectively). Seller assumes all responsibility for this listing. Alex Strekeisen - I vetrini della mia fantasia. Cleavages intersect at 90°. A variety of Anorthite A plagioclase feldspar with an albite : anorthite molar ratio ranging from 30 : 70 to 50 : 50. Alex Strekeisen - I vetrini della mia fantasia. Oligoclase is a somewhat rare variety of Albite and a member of the Plagioclase Feldspars of the Feldspar Group of minerals that includes Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone,Oligoclase, Orthoclase, Sanidine and Sunstone. Oligoclase is about 90-70% Albite and 10-30% Anorthite. Thin-section mount of oligoclase (triclinie) from Arendal, Norway, petrographic microscope slide. Has perfect cleavage on {001} and good cleavage on {010}. The cause of this optical phenomenon is lamellar structure caused by an exsolution process due to a miscibility gap. For viewing under polarized or transmitted light. Labradorite can display an iridescent optical effect (or schiller) known as labradorescence. Sericite PPL properties. An intermediate member of the Albite-Anorthite Series. Oligoclase was named in 1826 by August Breithaupt from the Greek words όλίγος and κλάσις meaning little and to break because the mineral was thought to have a less perfect cleavage than Albite. Relief: Low-Moderate positive Habit/Form: Well-formed tabular crystals with a roughly hexagonal outline are rare. Albite is the sodium-rich end member while Anorthite is the The Plagioclase Feldspars form a series between Albite and Anorthite. The composition of plagioclase feldspar is typically indicated by the general anorthite (% An) or albite (% Ab) fraction and is easily determined by measuring the refractive index or peel angle within the crushed particles by measuring the refraction angle under a thin section. 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