Crystallography : Triclinic, a = 8.17, b = 12.88, c = 14.16, a = 93.33°, b = 115.60°, g = 91.22°, Z = 8; space group P1; point group 1. Albite is one end member, containing sodium and no calcium. Also found as micaceous or tabular grains, or grains with irregular outline. To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website. Biotite #2 thin section (hFOV 2mm) GET 360° LIVE INTERACTION. The Plagioclase Feldspars form a series between Albite and Anorthite. First-order yellow colors are seen with anorthite. This twinning is the most characteristic identifying feature of plagioclase, and makes its identification easy when present. Habit : Anorthite is common as cleavable masses or irregular grains. Home Rocks and Minerals Plagioclase Feldspar (thin section) Reference URL Share . Anorthite thin section. Large number of pages viewed. The other end member, Anorthite, contains calcium and no sodium. Grains may be bent, particularly in metamorphic rocks. In thin section, plagioclase commonly shows the characteristic albite polysynthetic twinning. Relief: Moderate positive Habit/Form: Euhedral crystals are not uncommon, are usually tabular parallel to (001), and have a roughly hexagonal cross section. Add tags Comment Rate. Optical Properties : In thin section, anorthite is similar to other plagio-clase feldspars. Although some cross-hatched twinning may also occur in plagioclase, it is always very simple with only one or two cross twins per grain. Search for anorthite using. Anorthite is the rarest 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. Greater amounts of anorthite correlate to higher refractive indices. This optical mineralogy/petrography video is part of the "video atlas of minerals in thin section" library at https://www.rockptx.com. Plagioclase Feldspar (thin section) View Description . Anorthite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Biotite PPL properties. Max Birefringence: 0.007-0.013 : Maximum interference colors in thin section are usually first-order grey or white. May have zones or trails rich in inlcusions of quartz biotite etc which may show s or z shapes. Some specimens of labradorite exhibit a schiller effect which is a strong play of iridescent blue green red orange and yellow colors when moved under a source of incident light. Biaxial 1- 2, a = 1.577, b = 1.585, g = 1.590, d = 0.013, 2V = 78°. Some cross-hatched twinning may also occur in Plagioclase, it is always very simple with only or! Very simple with only one or two cross twins per grain group, isomorphous. 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