Because it is generally made up of very small crystals, its birefringence is irregular and generally low. It has a chemical formula of KFe32+AlSi3O10(OH)2. General Enstatite Information : Chemical Formula: Mg2Si2O6 : Composition: Molecular Weight = 200.78 gm Magnesium 24.21 % Mg 40.15 % MgO: Silicon 27.98 % Si 59.85 % SiO 2: Oxygen 47.81 % O: 100.00 % 100.00 % = TOTAL OXIDE Chromite is a spinel-type mineral, like magnetite, and has an extensive solid solution in the magnetite composition direction. This grain appears quite homogeneous in plane light, without concentric zones of inclusions that are commonly seen elsewhere. Birefringence and color may define zoning, and both increase with Fe3+ content. Annite= KFe 3 AlSi 3 O 10 (OH) 2. The red-brown biotite in this graphite- and garnet-bearing granite has high titanium and low Fe3+ content. Microcline from a peraluminous granite. Note the variable spacing of the twin domains, indicating that different volumes of the crystal nucleated different numbers of twin domains during inversion. In cross-polarized light you can see that the zones also have different birefringence, indicating they have different anorthite content. Strained quartz crystal in a metaluminous granite. Biotite usually dark green brown or black has a pale brown color under plane polarized light in this sample. Perthite from a metaluminous biotite granite. Initial CT findings and their evolution on sequential examinations may be useful in evaluating prognosis. Trust but verify: the value of acceptance testing. Dana, E.S. American Mineralogist, 58, 889-900. Oxidation turned some Fe2+ to Fe3+, precipitating magnetite by the reaction: olivine + O2 = magnetite + enstatite. A Becke line test tells you which phase is which: the Becke line goes into the higher index phase, albite. This example has birefringence zoning that is probably caused by igneous compositional zoning. The center inclusion has an irregular outer boundary, inside of which is a layer of liquid water, a layer of liquid CO2, and a central bubble of vapor (mostly CO2). Andalusite in hand sample (clicking on some images leads to larger versions) Andalusite (chiastolite) from a graphitic schist, Hamadan, Iran. The adjacent biotite has third order birefringence. Andalusite in quartz vein, Hamadan, Iran. Calcite has very high birefringence, so interference order is difficult to judge from the high-order pastel colors. Titanite birefringence is very high, making it difficult to determine interference color order from the high-order pastel interference colors normally seen. Lenses of high-index colorless material (titanite?) Indeed, it is rare to find a terrestrial plutonic rock without at least some apatite. Birefringence in the low to middle first order. It has a chemical formula of KFe32+AlSi3O10(OH)2. patents-wipo. Pale brown radiation halos can sometimes be visible around radioactive inclusions (but not really visible here). Biotite. Allanite in a metaluminous granite. As an alteration product it commonly forms as masses or veins of irregular, ragged crystals in Ca-rich plagioclase. Zoisite developed in pagioclase in an anorthosite. 2.1.3. Apatite crystals in norite. Swelling of the crystal as damage accumulates, and absorption of water, causes radial cracks that extend out into the surrounding minerals. Cordierite in a peraluminous granite. Biotite, peraluminous granite. annite definition: Noun (plural annites) 1. Fluid inclusions in quartz in alkali granite. High uranium layers accumulate more radiation damage and become less birefringent.  The index of refraction of a mineral is a measure of the speed of light in the mineral. Olivine is usually not associated with quartz (except in highly Fe-rich Mg-poor rocks), and is likely to be partly altered. These are photographs of a thin section of Granite (magnification 10X), perhaps the most common Igneous Rock we encounter. There are also peculiar paralellogram- and trapezoid-shaped patches of wormy opaque material in the olivine. Augite (thin section) View Description. In thin section it is clear to pale green to pale yellow, but does not show pleochroism, shows a generally low relief compared to minerals like olivine and pyroxene with which it is associated, and show very low order interference colors due to its low birefringence. Birefringencetends to be somewhat irregular in single grains because of compositional variations. Annite is monoclinic and contains tabular crystals and cleavage fragments with pseudohexagonal outlines. Left: Zircon oriented N-S. Zircon is usually colorless in thin section. Though it may seem obvious, opaque minerals are opaque in plane- and cross-polarized light, which differentiates them from isotropic, transparent minerals. The thin edge to the left of center of the first image has ~8th order birefringence. Because many twin domains nucleate throughout the crystal, there are large numbers of thin, spindly and discontinuous domains in the final microcline product. Plane-polarized light, field width is 0.6 mm. It is expressed as a ratio of the speed of light in vacuum relative to that in the given mineral. This is in contrast to the straight, and generally continuous twins in plagioclase. In optical mineralogy and petrography, a thin section (or petrographic thin section) is a laboratory preparation of a rock, mineral, soil, pottery, bones, or even metal sample for use with a polarizing petrographic microscope, electron microscope and electron microprobe. This is especially handy in tonalites, in which K-feldspar may be hard to find by other methods. Some of the larger crystals can be seen here to have first order birefringence. Discovered in 1792; … Phlogopite= KMg 3 AlSi 3 O 10 (OH) 2. 3, 82-125, https://en.wikipedia.org/w/index.php?title=Annite&oldid=990698744, Creative Commons Attribution-ShareAlike License. Find link is a tool written by Edward Betts.. searching for Thin section 219 found (333 total) alternate case: thin section Sericite (161 words) exact match in snippet view article find links to article abundant sericite. Here, K-feldpar was removed and quartz and plagioclase deposited in its place. 13 images. The actinolite is an inosilicato of the amphibole group It presents a solid solution with tremolite depending on the content of Ca and Fe (actinolite) and Ca and Mg (tremolite). Close-up showing the characteristic grid twinning in the microcline host (upper center and upper left) and albite twinning in the lamellae (lower center to center right). The larger crystals have up to middle first order birefringence. Biotite is monoclinic ,,g biaxial negative with 2V = 0-25°. Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite. Ateration to fine-grained material typically occurs along fractures, twin planes, or cleavages. It is more commonly euhedral than quartz in plutonic rocks. It is then mounted on a glass slide and then ground smooth using progressively … 9 images. 1) It tends to look dustier than quartz and feldspar, little black specks all over the surface, such as can be seen here. Unique Thin Section Posters designed and sold by artists. The largest grain of biotite contains a pelochroic halo (burn mark) around an included zircon. This allanite grain mostly has low birefringence, a result of radiation damage that has essentially turned the crystal lattice into a glass. Fluorite, of course, is isotropic. Press alt + / to open this menu. As layer repetition is probably common over the entire deposit, stratigraphical reconstructions are difficult and interpreting drill sections as simple stratigraphic sections is problematic. Garnet in a peraluminous granite. Thin-section bearings have a constant cross section within a given series, even for those with large bore diameters. (1892) Dana's system of mineralogy, (6th edition), 634. Kaydon thin section bearings. Lepidolite was named in 1792 by Martin Klaproth from the Greek words lepidos for scale, and lithos for stone, in allusion to its micaceous structure.. Varieties : Annite, phlogopite, and siderophilite are names given to end member Fe-, Mg-, and Al-biotite. Plagioclase, unzoned, in a hornblende diorite. Plane-polarized light, field width is 0.12 mm. Add tags Comment Rate. Calcite in an alkaline granite. Its relief is less than the pyroxenes but higher than any feldspar. Each thin section was first scanned in unpolarized light and then again between two sheets of crossed polaroid film aligned parallel to the thin section edges. When viewed under a microscope, this mineral may appear to stick out of the other minerals in the thin section. Plane/cross-polarized light, field width is 3 mm. and Wones, D.R. Specially selected thin sections of important rock-formingminerals are arranged by mineral group. These form the darkish, cloudy regions, especially in the grain to the lower right. The mineral is flexible and elastic; in thin sections : euhedral and anhedral.
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