Basalt thin section. Microcline. Rating. Select the collections to add or remove from your search, Alberta Women's Institutes - Collective Memory, Karvonen Films Natural History Collection, Thomas A. RELATED ARTICLES MORE FROM AUTHOR. Ultramafic thin section. You can find the explanation on the alkali feldspar page. Microcline is identical to orthoclase in many physical properties, and can be distinguished by x-ray or optical examination. In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). Syenite thin section. – Twinning: Typically displays albite twinning and pericline twinning. Crystal Data: Triclinic. ... Next article Microcline thin section. It is a fully ordered triclinic modification of potassium feldspar and is dimorphous with orthoclase. Microcline KAlSi3O8 °c 20 1M i nera lD t Pub sh g, v o . Edge Archives & Special Collections, δ = 0.005 - 0.008; Maximum interference color first order grey to white. Gabbro thin section. Common minerals that might be confused with K-feldspar and occur in similar rocks: Ultramafic thin section. Evje, Norway. Basalt thin section. When viewed under a polarizing microscope, microcline exhibits a minute … Perthitic exsolution lamellae of albite in microcline. Cleavage. Add tags Comment Rate. It is the dead giveaway of microcline. It easily forms from sani-dine or orthoclase as rocks cool from high. For some reason, almost everyone has trouble identifying microcline at first, so we thought we’d throw you a bone. Commonly exhibits banded perthitic intergrowths from exsolution of albite. Characteristally featureless in plane light, but the inverse Becke line highlighting technique described for orthoclase works just as well for microcline. It can be difficult to see cleavage in thin section due to microcline’s low relief. In this photo the thin section was rotated to obscure twinning. Because many twin domains nucleate throughout the crystal, there are large numbers of thin, spindly and discontinuous domains in the final microcline product. Microcline KAlSi3O8 °c 20 1M i nera lD t Pub sh g, v o . General Microcline Information : Chemical Formula: KAlSi3O8 : Composition: Molecular Weight = 278.33 gm Potassium 14.05 % K 16.92 % K 2 O: Aluminum 9.69 % Al 18.32 % Al 2 O 3: Silicon 30.27 % Si 64.76 % SiO 2: Oxygen 45.99 % O: 100.00 % 100.00 % = TOTAL OXIDE Magnification: 40x To explore this slide in PPL, click here: https://viewer.gigamacro.com/view/cgJwU…. In granite, syenite and pegmatites, i.e. perfect cleavage; usually not observed in thin section. Microcline Magnification: 40x Rock: Conglomerate NVCC slide AM 44. Can also display carlsbad twinning, simple twins, or lack twinning altogether. Photograph of thin section microcline showing the grid structure of twining under cross-polarized light. Amazonite (green microcline) Key optical features of K-feldspar in thin section: Colourless often cloudy Low relief Low order interference colours Polysynthetic twins (Microcline), simple twins (Sanidine & Orthoclase) Exsolution lamellae (Orthoclase and Microcline) . Orthoclase thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. Mineral. Microcline from a peraluminous granite. Microcline (KAlSi 3 O 8) is an important igneous rock-forming tectosilicate mineral.It is a potassium-rich alkali feldspar.Microcline typically contains minor amounts of sodium.It is common in granite and pegmatites.Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures than orthoclase. Microcline thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. … This combination leads to a grid pattern, hence microcline displays gridiron twinning. Point Group: 1: Prismatic crystals elongated along [001] or [100], perhaps the largest of any species, to 50 m and 13,500 t. A thin section image showing microcline grain in a coarse-grained sandstone from Estonia. Scanning electron micrograph of amazonite. “Tartan plaid”, “plaid”, “gridiron,” or “cross-hatch” twinning is a combination of albite and pericline twinning. Plane/cross-polarized light, field width is 6 mm. Microcline is distinguished in thin section from orthoclase (the medium temperature polymorph of potassium feldspar which is chemically identical to microcline) by the presence of tartan twinning. We wouldn’t normally circle the mineral in question on the slide.