Home Rocks and Minerals Muscovite (thin section) Reference URL Share . Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) 1 Olivine: forsterite Olivine: Forsterite, in marble. Download: … Geochemistry With a mineral that is too small for visual identification, the first step is making a thin section of the rock and determining the mineral composition. In the biotite-chlorite-amphibole composite microveins, tiny needles of biotite are present. Note the presence of the one perfect cleavage on the c-axis parallel section and its absence on the basal section. Thin sections are prepared in order to investigate the optical properties of the minerals in the rock. 4, 5). This tonalite gneiss, mostly composed of quartz, plagioclase and biotite is one of the oldest rocks in the U.S. (~3.5 Ga). Polars crossed, width of view 2.5 mm. Metamorphic rocks in thin section Contents Image scales (widest frame width) Al-silicates Other aluminous minerals Amphiboles Pyroxenes Sheet silicates Other metamorphic minerals 20x = 6 mm 40x = 3 mm 100x = 1 mm 200x = 0.5 mm 400x = 0.25 mm 1000x = 0.1 mm Al-silicates Andalusite in a muscovite-biotite schist.€ Note the diamond-shaped inclusion cloud to the bottom left, which is the … Muscovite and Biotite micas are easily indentified in thin section because they almost always exhibit "speckled extinction" in cross polarized light (see the top two and bottom two photomicrographs below). Additionally, where possible, multiple examples are provided to highlight how optical properties may vary with compositional diversity. Thin section of biotite in Morton gneiss, Minnesota River Valley. An image of Thin Section 54NC50, biotite granodiorite, in unpolarized light. Thin Section of Biotite (test) (cropped to Biotite).jpg 1.058 × 740; 237 KB Thin Section of Biotite (test).jpg 2.448 × 3.264; 1,53 MB Émeraude, biotite, quartz 7100.5405.jpg 1.970 × 1.514; 2,3 MB In Place. The colourless inclusions in the basal section are apatite. Note that these are colours seen in thin-section, not hand-specimen. An image of Thin Section 54NC50, biotite granodiorite, in polarized light. 19 - Minerals in Thin Section-University of North Carolina 20 - Minerals in Thin Sections-Humboldt State 21 - Online Mineral Museum 22 - QUT Mineral Atlas 23 - Ruff.Info 24 - Scandinavian mineral gallery 25 - UCLA - Petrography Thin-Sections 26 - WWW-MINCRYST. 64 East 12th Street, New York". It consists of a more-or-less random aggregate of biotite flakes. Parry and Downey con-sidered the possibility that "biotite is replaced by an equiv-alent volume of chlorite", although they also state that sphene is an alteration product. This granulite facies schist has coarse sillimanite prisms that can be seen in long section and in their diamond-shaped cross sections. No contact with olivine was found in the thin sections. ), now altered to quartz-biotite aggregates, in a fine grained biotite (annite) matrix. Pre-Devonian. Printed label has "Monte Somma, Vesuvius, Italy" crossed out, with "New York Island, NY" neatly penned in. The thin section also contains excellent examples of the rare mineral jimthompsonite, which appears to have replaced (pseudomorphed) earlier porphyroblast mineral in this rock. There are two ways. The latter will always be much darker and more intense than thin section colours. Tracings of thin sections and photomicrographs showing muscovite-free regions produced by reactions in the matrix around sillimanite segregations are illustrated in Foster (1977, Figs. It appears sometimes in fairly well-formed thin, platy crystals and sometimes as ragged flakes with dimensions that range from less than 0.1 mm up to 3.0 mm in phenocrysts. Minerals in Thin Section, Dexter Perkins and Kevin R. Henke. 4.7.84G. Biotite, usually dark green, brown, or black, has a pale brown color under plane-polarized light in this sample. that is biotite-free. 2 Olivine: forsterite Olivine: Forsterite, in marble. Address listed as "No. Fish Canyon Tuff . Add tags Comment Rate. the reaction products appear in thin section to occupy all of the original biotite volume. Editors: Elizabeth Thomas (2003), Andrea Gohl (2007) and Emma Hall (2013). In thin section this diorite contains laths of plagioclase feldspar often 2-3 millimetres long, and minor amounts of quartz. Age. Muscovite (thin section) View Description. University students, faculty, and staff can access the thin section samples at the University of Nevada, Reno Libraries' Digital Archive, in the Great Basin Science Sample and Records Library, Nevada Bureau of Mines and Geology digital collection . Thin section 2. Plates 5.3, 5.4, 5.7, and 5.9 show biotite in thin section. L504 thin section, cross-polarised light. and biotite: after Perkins, 324: Chlorite in Hand Sample. Thin section of biotite in Morton gneiss, Minnesota River Valley. This label dates to 1893-1898. Blades of sillimanite are present in some bands. This was accomplished by examination of thin sections cut (1) parallel to foliation, and (2) perpendicular to foliation in both lineation-parallel and lineation-normal sections (all photomicrographs in this paper are shown in plane-polarized light). Some minor green … Cross-polarized light, field width is 6 mm. Introduction to Optical Mineralogy, William D. Nesse, 1991. Search for Biotite using: PPL. 6). Strongly developed planar fabric made up of platy biotite mica and muscovite mica grains and lenses of quartz grains. There is a smaller book to the left. These sheets of biotite are as thin as in the first muscovite photo above, but they are black and shiny, not silvery and shiny. Note quartz-feldspar and biotite-muscovite bands. Usually, the perfect basal cleavage of the micas is evident in thin section. Fabric wraps around large, euhedral garnets, typically ~2mm across. Chlorite slickensides in Brallier Formation shale Scanning electron micrograph of chlorite slickensides in Brallier Formation shale Chlorite in Balls Bluff siltstone Chlorite porphyroblasts in either Popes Head Formation schist or Station Hills phyllite (there is some argument about this one) Chlorite in Castner marble. When visible, cleavage lines are usually straight and parallel but very occasionally in Cheviot biotite, they can appear wavy or kinked. The biotite appears as small black 'flecks' on the surface of the specimens. Plane/cross-polarized light, field width is 3 … Biotite Size: 6.5x8.5cm A single black Biotite crystal 6.5 x 8.5 with no matrix. Plane-polarised light, width of view 2.5 mm. Elsewhere in the thin section relics of garnet remain in these aggregates, which are said to pseudomorph the original mineral. Origin and Occurrence. A camera lucida drawing that shows a biotite-free mantle adjacent to partially replaced kyanite is shown by Hietanen (1963, Fig. Rock Thin Section Preparation for Limestone. Feldspars, clinopyroxene, garnet, biotite and hornblende. Pseudomorph of biotite after garnet. Biotite has a high birefringence which can be masked by its deep intrinsic color. 3 Zircon Zircon, with distinct core and rim zones, in aluminous granulite. Optical Properties : Brown, red, or green in thin section, biotite exhibits strong pleochroism, perfect cleavage, bird s-eye ex-tinction, and parallel or near-parallel extinction. c-axis parallel section (left) and subhedral basal section (right) of brown biotite. The colourless inclusions in the basal section are apatite. In Time. The brown patch at the centre of the field of view has the regular outline of a garnet. Hand Specimen. The featured minerals are cross referenced to PPL and XP scans of the source thin section and to accompanying microprobe data, to provide for greater petrologic context. The mafic minerals are dominated by high relief pyroxene with it's characteristic cleavage, and common biotite which exhibits some pleochroic haloes caused by zircon inclusions. Biaxial 1- 2, a = 1.57, b = 1.60, g = 1.61, d = 0.04, 2V = 0° to 32°. The lower second order blue birefringence can be seen in the long sections. It exhibits high interference colors in cross-polar light just as muscovite, but has a lower birefringence than muscovite. Plane-polarised light, width of view 0.25 mm. This tonalite gneiss, mostly composed of quartz, plagioclase and biotite is one of the oldest rocks in the U.S. (~3.5 Ga). Biotite granite is a coarse grained, felsic intrusive rock, the minerals which make up a granite are typically quartz, feldspars and micas. This large book of biotite (~ 6" across) shows the 6-sided shape of perfect biotite crystals. PPL. See label photo. Biotite big square, matrix probably mostly fine-grained plagioclase, other gray crystals are either untwinned feldspar or possibly quartz, and the colorful diamondish grains are the amphibole (usually hornblende in andesites/dacites). Note growth of fine-grained chlorite along the discrete shear bands. Width of picture is 5 mm. (iv) RI: the total range of refractive index shown by the mineral with this coulour is shown: This covers any range due to compositional variation by solid solution, as well as the two or three refractive indices of anisotropic minerals. In plane-polarized light (left), biotite is brown-green to brown, depending on the orientation of … Search for Biotite using: To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website. Fish Canyon Tuff . Most of the biotite needles are too small to be optically identified or quantitatively analyzed, and their presence was detected by K-rich compositions. This means that biotite in standard thin sections rarely goes completely extinct. In thin section, biotite exhibits moderate relief and a pale to deep greenish brown or brown color, with moderate to strong pleochroism. Biotite is unstable during the deformation and transformed to chlorite. 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