This picture of Muscovite shows the characteristic Solid solution mineral; substitutions can occur for K, [VI]Al, (OH) and in tetrahedral sites. The bright 2nd order colors also contrast If the interference colors compound the sample is length slow, if they subtract the sample is length fast. to damage during slide preperation, but it is also one method of (larger 2V), birds-eye extinction and cleavage are also distinctive. small cleavage lines as well as the differences between Muscovite and Well-formed crystals are sometimes called “books” in reference to their flaky nature. Biotite #2 thin section (hFOV 2mm) GET 360° LIVE INTERACTION. This optical mineralogy/petrography video is part of the "video atlas of minerals in thin section" library at https://www.rockptx.com. muscovite crystals found in granite such as this one. Pleochroism: Weak when colored. Association: Quartz, plagioclase, potassic feldspar, biotite, tourmaline, topaz. Muscovite KAl2(Si3Al)O10(OH;F)2 ... yellow, rose-red; commonly colorless in thin section, but may be pale yellow, green, red-brown. identifying muscovite under the microscope. heat; and as a fireproofing material. Grains may be bent, particularly in metamorphic rocks. No pleochroism. U.C.L.A Petrographic Workshop - Muscovite. Muscovite (var. the crystal is close to extinction. Used in the manufacturing of paint, joint compound, plastics rubber, asphalt roofing, cosmetics, drilling mud. Well formed crystals are tabular and have pseudohexagonal outlines. Parallel to cleavage in all orientations, BIRD’S EYE, The maximum extinction angle is less than 3 degrees. used for this purpose in the United States is imported from India. related felsic rocks. Muscovite in slate (fine grained) with pale green chlorite, quartz and plagioclase Note: Small colourless muscovite in low grade rocks is typically thinner than 30 µm section and so have lower order interference colours, or colours that are higher order in the thicker centre of grains is common in granites and granitic pegmatites. The stage is then rotated another 45 degrees so the crystal is lying NE-SW and the gypsum plate is inserted. Streak: White. Colorless or shades of light green, red, or brown in hand sample; colorless in thin section. Muscovite is very common in large variety of metamorphic rocks including It is an essential rock-forming mineral present in igneous, metamorphic, and sedimentary rocks. feather-like lines could be due to deformation and is often seen in [online] Available at: https://geologyscience.com/minerals/muscovite/ [29th November 2020 ], Economically Important Metal Concentrations in Earth’s Crust, Porphyry Deposits: General characteristics and modeling, https://geologyscience.com/minerals/muscovite/, Thick specimens often appear to be black, brown, or silver in color; however, when split into thin sheets muscovite is colorless, sometimes with a tint of brown, yellow, green, or rose. as a transparent material, isinglass, for stove doors, lanterns, etc. Muscovite thin section. Also very common in metamorphic rocks, as gneiss and schist, forming the chief constituent in certain mica-schists. In the USA, at Mt. Igneous occurances include granite, grandorite, aplite, pegmatite and related felsic rocks. Optic Sign: Biaxial (-) Muscovite is length slow: 2V: 28-47 o : Optic Orientation: Z=b X^c = +1 o to +4 o Y^a = +1 o to +3 o O.A.P. Igneous occurances include granite, grandorite, aplite, pegmatite and This property is observed when the stage is rotated until the crystal is exinct. Another view of PE-19 showing textures at extinction. Finite is a name given to the micaceous alteration product of various minerals, which corresponds in composition more or less closely to muscovite. shiny luster; as a lubricant when mixed with oils; as a nonconductor of Colour and Pleochroism. Muscovite is a potassium-rich mica with the following generalized composition…. bird's eye extinction. Biotite. Around Nellore, Andhra Pradesh, India, in commercial deposits which may contain huge crystals. More often found as micaceous flakes or tablets with irregular outlines. Sericite is name given to very fine, ragged grains and aggregates of white mica – usually muscovite – produced by the alteration of feldspars or other minerals. in thin section. the thumbnail to see a rollover image of the bird's eye texture when Many of the small parts used for electrical insulation are built up of thin sheets of mica cemented together. Muscovite is the most common mineral of the mica own family. with irregular outlines. Muscovite sheets have a pearly to vitreous luster on their floor. The striking similarity between the inclosing granite and aplite is sufficiently shown in the chemical analyses of the rocks given below. Key optical features of muscovite in thin section: Colourless Single cleavage Moderate Relief High order interference colours Straight extinction Common minerals that might be confused with muscovite and occur in similar rocks: Not many! Note the Home Atlas of … Click Scrap mica, or the waste material in the manufacture of sheet mica, is Orientation: Z = b; X ^ c = 0 ±{5 ; Y ^ a = 1±{3±. Muscovite in thin section from sample PE-19. Well-formed crystals are sometimes called "books" in reference to their flaky nature. Muscovite is very common in large variety of metamorphic rocks including slate, schist, phyllite, gneiss, hornfels and quartzite. This variety, known as sencite, is usually the product of alteration of feldspar. Another view of PE-19 showing textures at extinction. Click the thumbnail to view a rollover of the interference figure. Click to see a rollover image that shows the twinning as the thin section is rotated and gives a better view of the "birds-eye" extinction. Aluminum is sometimes replaced by magnesium, iron, lithium, chromium, or vanadium. Colorless in thin section. Muscovite from sample DR-4 in plane polarized light. Muscovite in thin section from sample PE-19. Click on the thumbnail to see a rollover image in cross-polars. Muscovite shape and interference colours. Distinguished from phlogopite by not being decomposed in sulfuric acid and from lepidolite by not giving a crimson flame. WWW Images No pleochroism. (2020). Colorless or shades of light green, red, or brown in hand sample; colorless From Slyudyanka, near Lake Baikal, Siberia, and at Mursinka, Ural Mountains, Russia. Muscovite in Thin Section Thin Section GigaPans. Relief: Moderate positive Habit/Form: Euhedral crystals are not uncommon, are usually tabular parallel to (001), and have a roughly hexagonal cross section. Muscovite in thin section from sample pe 19. Muscovite has a widespread occurance and is characteristic of sedimentary, igneous and metamorphic rocks. Name: From \Muscovy glass,” for an occurrence in the old province of Muscovy, Russia.