Muscovite thin section. Home Atlas of … Luster: Vitreous to pearly or silky. Muscovite - K 2 Al 4 [Si 6 Al 2 O 20](OH,F) 4 The name muscovite comes from Muscovy-glass, a name given to the mineral in Elizabethan England due to its use in medieval Russia as a cheaper alternative to glass in windows. 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 This picture of Muscovite shows the characteristic Note the Muscovite in the basic aluminium-potash mica with basic formula K 2 Al 4 [Si 6 Al 2 O 20](OH,F) 4. Well formed crystals are tabular and have pseudohexagonal outlines. Muscovite sample W-12 in cross-polarized light. Click on the thumbnail for a larger, rollover version. Igneous occurances include granite, grandorite, aplite, pegmatite and related felsic rocks. Most of the mica Relief: Moderate positive Habit/Form: Euhedral crystals are not uncommon, are usually tabular parallel to (001), and have a roughly hexagonal cross section. Parallel to cleavage in all orientations, BIRD’S EYE, The maximum extinction angle is less than 3 degrees. This variety, known as sencite, is usually the product of alteration of feldspar. This optical mineralogy/petrography video is part of the "video atlas of minerals in thin section" library at to damage during slide preperation, but it is also one method of Used in the manufacturing of paint, joint compound, plastics rubber, asphalt roofing, cosmetics, drilling mud. ('01), Jenny McNicholas ('11), Kathryn Durkin ('12), Theo Sweezy ('14). Colorless or shades of light green, red, or brown in hand sample; colorless Well displayed, controls fragment orientation. The In crossed polarized light, the Muscovite shows the bright 2nd order thus be pressed into shape before the cement hardens. Parallel to cleavage in all orientations, BIRD'S EYE, The maximum extinction angle is less than 3 degrees. In some schistose rocks it occurs in the form of fibrous aggregates of minute scales which have a silky luster, but which do not show plainly the true nature of the mineral. Absorption: Faint; Y ' Z > X. is common in granites and granitic pegmatites. Muscovite, PPL Mica, near Paris, Oxford Co., and elsewhere in Maine; large crystals from Pennsbury, Chester Co., Pennsylvania; at Amelia, Amelia Co., Virginia; crystals from near Shelby, Cleveland Co., North Carolina; in the Black Hills, in Pennington, Lawrence, and Custer Cos., South Dakota; and from the Harding mine, Dixon, Taos Co., New Mexico. 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. Biotite #2 thin section (hFOV 2mm) GET 360° LIVE INTERACTION. No pleochroism. Muscovite in thin section from sample PE-19. Especially characteristic of pegmatite dikes, and found lining cavities in granites, where it has evidently been formed by the action of mineralizing vapors during the last stages of the formation of the rock. Click the thumbnail to view a rollover of the interference figure. Colorless or shades of light green, red, or brown in hand sample; colorless in thin section. Muscovite has a widespread occurance and is characteristic Muscovite, plane polars Muscovite, crossed polars Fine-grained muscovite with chlorite (green), plane polars Fine-grained muscovite with chlorite, crossed polars Muscovite with biotite and garnet in Maidens gneiss, plane polars Muscovite with biotite and garnet in Maidens gneiss, crossed polars. Click on the thumbnail to see a rollover image in cross-polars. Well-formed crystals are sometimes called "books" in reference to their flaky nature. Name: From \Muscovy glass,” for an occurrence in the old province of Muscovy, Russia. The c-axis of this crystal is nearly vertical. Biotite (strongly coloured), Common alteration product: None. Dispersion: r > v; weak. A Association: Quartz, plagioclase, potassic feldspar, biotite, tourmaline, topaz. Optical Class: Biaxial ({). This property is observed when the stage is rotated until the crystal is exinct. Muscovite is a widespread and very common rockforming mineral. Like other micas it with no trouble cleaves into skinny transparent sheets. Characteristic of deep-seated siliceous igneous rocks as granite and syenite. Finite is a name given to the micaceous alteration product of various minerals, which corresponds in composition more or less closely to muscovite. In Methuen and Calvin Townships, Ontario, Canada. Muscovite has a Mohs hardness of 2–2.25 parallel to the face, 4 perpendicular to the and a specific gravity of 2.76–3. Monazite Xpl Note The Extreme Birefringence And Diamond Shape Rocks And Minerals Geology Minerals . Colorless or shades of light green, red, or brown in hand sample; colorless in thin section. the thumbnail to see a rollover image of the bird's eye texture when identifying muscovite under the microscope. They may Biotite (darker in color and is pleochroic in ppl), Talc (smaller 2V), Pyrophyllite Muscovite has a widespread occurance and is characteristic of sedimentary, igneous and metamorphic rocks. Bird's eye texture could be be due In this formula potassium is sometimes replaced by other ions with a single positive charge such as sodium, rubidium, or cesium. The green muscovite in the center of the image displays twinning, as does the piece to its left. Distinguished from phlogopite by not being decomposed in sulfuric acid and from lepidolite by not giving a crimson flame. used for this purpose in the United States is imported from India. shiny luster; as a lubricant when mixed with oils; as a nonconductor of Solid solution mineral; substitutions can occur for K, [VI]Al, (OH) and in tetrahedral sites. Included grains of zircon or other radioactive minerals may form pale pleochroic halos in surrounding muscovite. Muscovite from sample DR-4 in plane polarized light.