It has a hardness of 6.5 and exhibits many optical qualities such as pleochroism, high relief and frequent lamellar twinning. It has parallel extinction relative to its usual long crystal dimension (the b direction), but inclined excinction, looking down b relative to its {001} cleavage. Chlorite minerals are found in rocks altered during deep burial, plate collisions, hydrothermal activity, or contact metamorphism. Mg-rich variety known as Sismondine 0000000716 00000 n Large porphyroblasts of chloritoid exhibit greenish brown/blue pleochroism, blocky shapes and poor cleavage. well as in hydrothermal environments. Sue Scheufele ('05), Louisa Hall ('15) Data Sources: Deer, W. A., R. A. Howie, and Jack Zussman. Results from low to medium grade regional metamorphism as 276 0 obj <> endobj Thin section of Chlorite Chlorite. 0000011353 00000 n 0000011207 00000 n {110} good The thin section illustrates the folded metasedimentary banding, with fine grained quartz, muscovite, and chlorite. 0000001553 00000 n First Recorded Locality: ⓘ Gmina Strzegom, Świdnica County, Lower Silesian Voivodeship, Poland. 0000010999 00000 n This rollover shows chloritoid, the elongate mineral, in both plane polarized light and cross polarized light. %PDF-1.3 %���� Mn-rich variety known as Ottrelite Epidote - Ca 2 (Fe,Al) 3 (SiO 4) 3 (OH) Named in 1801 by Rene Just Hauy from the Greek "Epidosis" = "increase" because the base of the rhombohedral prism has one side larger than the other. Both the fibrous and traditional forms of sillimanite are common in metamorphosed sedimentary rocks. Chlorite in Hand Sample. 0000002947 00000 n Twinning common on {001}. Key optical features of chlorite in thin section: Green to Pale green Pleochroic Single cleavage and straight extinction Moderate Relief Low order (almost isotopic) and anomalous interference colours (see below) . The largest grain of biotite contains a pelochroic halo (burn mark) around an included zircon. Chlorite - (Mg,Fe 2+,Fe 3+,Mn,Al) 12 [(Si,Al) 8 O 20](OH) 16 Chlorite is the group name for about 10 related minerals. 0000005116 00000 n Two polymorphs, one monoclinic, the other, triclinic. Simple twinning is relatively common. It has parallel extinction relative to its usual long crystal dimension (the b direction), but inclined excinction, looking down b relative to its {001} cleavage. Chlorite. {010} parting, (x) colorless, olive green, gray beta =  Common associative minerals are muscovite, chlorite, garnet, staurolite and kyanite. Distiguishing factors are the lack of birds eye extinction and the two distinct cleavages. 276 21 Large porphyroblasts of chloritoid exhibit greenish brown/blue pleochroism, blocky shapes and poor cleavage. Chlorite in Schist . 0000011103 00000 n x�b``�c``Nc`c`��� Ȁ ��@Q��=IJ-+�ޡ\���tr�u�3S�jY�]�[email protected]��'O�,����κ๕?�/���Ib��y�y�μ3��{���`�@�L����+��a`����= � s8oPh�ñ�%�ɠQ����U���1�螵g��#12h4�8p)�L The width of the field of view is 7.75 mm (Sample DR-2b). Mineral structure: Sheet silicate. 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. Twinning common on {001}. <<3D7803B61383DF4C9F9D886EE01949E2>]>> 0000004053 00000 n 296 0 obj<>stream Crystal habit and cleavage distinguish hornblende from dark-colored pyroxenes. gamma =, 1.713-1.730 Chlorite XPL properties . There are also books of chlorite visible at … 0000007473 00000 n 0000000016 00000 n Rock-forming minerals associated with Chlorite: Quartz, Muscovite, Amphibole, Biotite. Although commonly light yellow-green in thin section, it may be colorless. The thin section illustrates the folded metasedimentary banding, with fine grained quartz, muscovite, and chlorite. 1.719-1.734 Needle-shaped minerals, probably rutile, are present locally. Common mineral in Pelites (Low grade), Metabasic rocks (low grade), or the alteration products of Fe-rich minerals. This sample is a biotite-cordierite-orthopyroxene gneiss from near Sioux Lookout, Ontario.The field of view, about 2 mm across, is dominated by olive-green-brown biotite.. alpha = 0000009745 00000 n 0000011376 00000 n 0000008601 00000 n Crystal System: Monoclinic. 0000011318 00000 n In the crossed-polarizer view below, the chlorite stands out because of its anomalous extinction colors. trailer Hide all sections | Show all sections. ... A cluster of chloritoid crystals in thin section (Sample CH-8b). Rocks that commonly contain abundant chlorite include greenschist, phyllite, chlorite schist, and greenstone. Not visible in thin section. 0000001662 00000 n Chlorite in Thin Section 0000006346 00000 n In thin section the cleavage generally is defined by small white micas, opaque minerals, oxides and calcitic material. Most are optically positive but negative minerals have been found. startxref Cleavages at 56 and 124 degrees which form a distinctive diamond shape in cross section. 0000010888 00000 n About Chlorite GroupHide Hardness: 2 - 2½. 0000001249 00000 n l�Pin�. Although commonly light yellow-green in thin section, it may be colorless. Forms series with Carboirite, Pseudohexagonal tabulate crystals are rare, {001} perfect Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay ... (note one grain with 56-124 cleavage just below left center). Common minerals that might be confused with chlorite and occur in similar rocks: Not visible in thin section. 0 Cleavage: Perfect in one direction {001}; in basal sections (z-axis) has no cleavage. (z) colorless, yellow-green, greenish brown, Refractive Indices The morphology of the cleavage varies from slaty cleavage to domainal cleavage to crenulation cleavage (Hobbs et al. Identification Tables for Common Minerals in Thin Section These tables provide a concise summary of the properties of a range of common minerals. (y) blue-gray, indigo, blue-green They are also found as retrograde minerals in igneous and metamorphic rocks that have been weathered. 1976, p. Chlorite is an important constituent of many contact and regional metamorphic rocks of low to medium grade, usually with temperatures of to 400 degrees C and pressures up to a few Kb. Within the tables, minerals are arranged by colour so as to help with identification. 0000001095 00000 n 0000001198 00000 n �0�`b�fm�R`M` However, the term chlorite can be used both to describe the group in general, or as a specific term to describe any green member of the Chlorite group whose exact identity is not practical to be determined. Note the lamellar twinning present in xpl. Cleavage {001} perfect {110} good {010} parting. Alex Strekeisen - I vetrini della mia fantasia. 1.723-1.740. Hornblende is easly confused with biotite. Cleavage {001} perfect {110} good {010} parting. %%EOF Properties - In hand specimen, chlorite is recognized by its green color, micaceous habit and cleavage, and association with other minerals like actinolite and epidote. It also found in amygdules, fractures in altered volcanic rocks, hydrothermal vein deposits and soils. A common variety of sillimanite is known as fibrolite, so named because the mineral appears like a bunch of fibres twisted together when viewed in thin section or even by the naked eye. There are also books of chlorite visible at the edges of the chloritoid … In thin section, Chlorite shows low relief and low birefringence, with a characteristic midnight blue to black anomalous interference color.

chlorite cleavage thin section

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