Crystallography : Triclinic, a = 8.14, b = 12.79, c = 7.16, a = 93.17°, b = 115.85°, g = 87.65°, Z = 4; space group P1; point group 1. Damage produced during thin section grinding causes speckles of light in the biotite, where the crystal lattice has been deformed. drag2 - RMB Resize/Rotate Plates 5.7 and 5.8 show plagioclase in thin section. html += printReadyElem.innerHTML; Blocky - Crystal shape tends to be equant (e.g. From the Latin, albus, in allusion to the common color. Help on Above. RMB - Cycle Display Modes Rare euhedral crystals are prismatic, tabular, or bladed. S - Stereo Pair on/off drag1 - LMB Manipulate Structure Biaxial (+), a=1.528-1.533, b=1.5317-1.53685, g=1.538-1.542, bire=0.0090-0.0100, 2V(Calc)=76-82, 2V(Meas)=45. Relief: Low-moderate negative/positive (Albite-Anorthite series) Habit/Form: Plagioclase commonly occurs both as euhedral and anhedral grains. To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website. lelang barang bekas kantor: What's up, every time i used to check webpage posts here early in the morning, a... watches shop: Incredible points. } else Warning: this large pop-up is very compute intensive and may not work well with some computers. Low albite’s structure is similar to that of low microcline; high albite’s struc-ture is more disordered. Occurrence and associations : The most abundant mineral of the Earth’s crust, plagioclase feldspars are found in a wide variety of igneous, metamorphic, and, less commonly, sedi-mentary rocks. Granular - Generally occurs as anhedral to subhedral crystals in matrix. Albite, defined as plagio-clase with greater than 90% NaAlSi3O8, is found in silicic igneous rocks such as granite, syenite, trachyte, or rhyolite, where it associates with quartz and orthoclase. } _uacct = "UA-3067463-1"; { Color: Colorless, frequently cloudy due to incipient alteration Pleochroism: Add tags Comment Rate. } a = 8.144, b = 12.787, c = 7.16, Z = 4; alpha = 94.266°, beta = 116.583°, gamma = 87.667° V = 664.40 Den(Calc)= 2.63. M - Menu Dispersion relatively weak. At very high temperature a completely disordered albite, called monalbite be-cause it is monoclinic, is stable. Albite is a very common mineral, and is an important rock-forming mineral. Plate 6.8 shows rare euhedral albite. Dbl Clk - Start-Stop Rotation It is sim-ilar to K-feldspar and superficially similar to quartz. Rockhounds Discussion Group on Yahoo Groups Bourg d'Oisans and Isere, France. Habit : Masses or subhedral grains are common. Hand Specimen identification: Cleavage, hardness, luster, and association help identify anorthite, but it can be …, Your email address will not be published. Add tags Comment Rate. return; Drag2 - Resize February 27, 2018 Home Rocks and Minerals Plagioclase Feldspar (thin section) Reference URL Share . } Crystals are usually tabular parallel to (010) and elongate parallel to the c or a axis. Scale: 4 x 3 x 2 cm. Plane//cross-polarized light, field width is 6 mm. This is called "incomplete extinction" or sometimes "birds eye maple extinction". if (gAutoPrint) { Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) Atlas of Metamorphic Minerals. Great arguments. Optical Properties : In thin section, plagioclase shows no color, has low relief, and exhibits gray interference colors. Cleavage/Fracture : perfect (001), good (010), poor, Luster/Transparency : vitreous/translucent. if (printReadyElem != null) Related Minerals : Albite is closely related to the other, more calcic pla-gioclase feldspars, and to the other alkali feldspars (orthoclase, sanidine, and microcline). Fluorescent, Short UV=herry-red blue, Long UV=white. Scale: 17 x 15 x 7.5 cm matrix. { Ask-A-Mineralogist from the Mineralogical Society of America carbonates in thin section unless stained. Albite twins are prominent, and some small pericline twins can also be seen. urchinTracker(); Print or Cut-and-Paste your Albite Specimen Label here : Location: Taquaral, Minas Gerais, Brazil. 4.7.84H. var html = '\n\n'; Drag1 - Manipulate Crystal printWin.print(); Keyboard "); Comments: Colorless, lustrous blocky albite crystals to 3 cm in size with a thick dusting of micaceous green micro chlorite. H - Help Screen Crystals in igneous rocks often rectangular laths. 570 Views. Albite twins give plagioclase the characteristic polysynthetic twinning that is often visible as fine striations in hand specimen and as stripes in thin section. NEIGC84-A5-5C. else Polars crossed, field of view 2.5 mm. Plane/cross-polarized light, field width is 3 mm. 6.6.4.2 pH dependence of the dissolution kinetics of feldspars. Varieties : Clevelandite is a form of albite, typified by curved plates, found in pegmatites. Figure 6.29 shows that the dissolution rate of albite is strongly dependent upon pH and temperature. P - Polyhedra On/Off Link to . In thin section, plagioclase commonly shows the characteristic albite polysynthetic twinning. It has already been mentioned that the colors of plagioclase, even if the thin section is thicker than usual, seemed to indicate a high anorthite/albite ratio. Feldspar - Feldspar - Identification of specific feldspars: Alkali feldspars can often be distinguished from plagioclase feldspars because most grains of the latter exhibit albite twinning (see above Crystal structure), which is manifested by parallel lines on certain cleavage surfaces, whereas grains of alkali feldspars do not.

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