This combination leads to a grid pattern, hence microcline displays gridiron twinning. Cleavage. Microcline, crossed polars, Microcline. It is the dead giveaway of microcline. RELATED ARTICLES MORE FROM AUTHOR. Microcline at webmineral.com Plane//cross-polarized light, field width is 6 mm. For some reason, almost everyone has trouble identifying microcline at first, so we thought we’d throw you a bone. ... Next article Microcline thin section. Photograph of thin section microcline showing the grid structure of twining under cross-polarized light. Plagioclase Feldspar (thin section) View Description. Microcline at mindat.org, Scanning electron micrograph of amazonite. Twinning: Carlsbad, Colour and Pleochroism. Ultramafic thin section. Syenite thin section. We wouldn’t normally circle the mineral in question on the slide. Orthoclase thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. Characteristally featureless in plane light, but the inverse Becke line highlighting technique described for orthoclase works just as well for microcline. Because many twin domains nucleate throughout the crystal, there are large numbers of thin, spindly and discontinuous domains in the final microcline product. Usually colorless, pale coloration possible in … Microcline Varieties : When colored a deep green, microcline is given the name amazonite shown in Figure 5 (refer also to Plate 8.3). Microcline is also common in metamorphic rocks in gneisses, and in sedimentary rocks in arkoses and conglomerates. In the field the indicators are color, transparency, occurance and luster. In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). – Twinning: Typically displays albite twinning and pericline twinning. Microcline (thin section) Type. Home Rocks and Minerals Plagioclase Feldspar (thin section) Reference URL Share . It is characterized by cross-hatched (tartan) twinning in crossed polars. It easily forms from sani-dine or orthoclase as rocks cool from high. However, the polysynthetic twinning of plagioclase is clearly defined and does not pinch and swell as the tartan twinning of microcline does. Crystal Data: Triclinic. A thin section image showing microcline grain in a coarse-grained sandstone from Estonia. In plagioclase feldspar polysynthetic twinning in two directions can mimic microcline's tartan twinning. Basalt thin section. 4.7.84H. Microcline displaying its distinctive “tartan plaid” twinning in cross polarized light. … Can also display carlsbad twinning, simple twins, or lack twinning altogether. Scanning electron micrograph of amazonite. It is a fully ordered triclinic modification of potassium feldspar and is dimorphous with orthoclase. Evje, Norway. Microcline from a peraluminous granite. Gabbro thin section. 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. Select the collections to add or remove from your search, Alberta Women's Institutes - Collective Memory, Karvonen Films Natural History Collection, Thomas A. Commonly exhibits banded perthitic intergrowths from exsolution of albite. Microcline may be chemically the same as monoclinic orthoclase, but because it belongs to the triclinic crystal system, the prism angle is slightly less than right angles; hence the name "microcline" from the Greek "small slope." It is the dead giveaway of microcline. Microcline KAlSi3O8 °c 20 1M i nera lD t Pub sh g, v o . 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) . “Tartan plaid”, “plaid”, “gridiron,” or “cross-hatch” twinning is a combination of albite and pericline twinning. Orthoclase thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. Add tags Comment Rate. Magnification: 40x To explore this slide in PPL, click here: https://viewer.gigamacro.com/view/cgJwU…. perfect cleavage; usually not observed in thin section. Rating. In this photo the thin section was rotated to obscure twinning. Occurrence and associations : Microcline is common in many kinds of silicic igneous rocks, sediments such as arkoses, and a va-riety of metamorphic rocks. Microcline is an essential component of many rocks, especially granite, syenite, pegmatite (Table 4.1) and gneisses (Table 6.1). The mineral's low relief, lack of color and tartan twinning are characteristic. 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 Microcline is identical to orthoclase in many physical properties, and can be distinguished by x-ray or optical examination. Syenite thin section. You can find the explanation on the alkali feldspar page. Name. In granite, syenite and pegmatites, i.e. “Tartan plaid”,  “plaid”, “gridiron,” or “cross-hatch” twinning is a combination of albite and pericline twinning. In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). Perthitic exsolution lamellae of albite in microcline. 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. Crystal Data: Triclinic. Microcline KAlSi3O8 °c 20 1M i nera lD t Pub sh g, v o . Basalt thin section. ... Next article Microcline thin section. Plane/cross-polarized light, field width is 6 mm. Width of view 3 mm. Common minerals that might be confused with K-feldspar and occur in similar rocks: Microcline, plane polars Edge Archives & Special Collections, δ = 0.005 - 0.008; Maximum interference color first order grey to white. Gabbro thin section. Mineral. It can be difficult to see cleavage in thin section due to microcline’s low relief. Width of sample 6 cm. Amazonite (green microcline) Point Group: 1: Prismatic crystals elongated along [001] or [100], perhaps the largest of any species, to 50 m and 13,500 t. Microcline thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. Ultramafic thin section. Magnification: 40x Rock: Conglomerate NVCC slide AM 44. RELATED ARTICLES MORE FROM AUTHOR. Magnification: 40x To view this grain in XPL, click here: https://youtu.be/183abevrp7U To explore this slide in PPL, click here: https://viewer.g…, Microcline displaying its characteristic plaid twinning. When viewed under a polarizing microscope, microcline exhibits a minute … Point Group: 1: Prismatic crystals elongated along [001] or [100], perhaps the largest of any species, to 50 m and 13,500 t. Cleavable to granular, massive. To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website. Microcline. 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