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