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