Granular - Generally occurs as anhedral to subhedral crystals in matrix. Also found as micaceous or tabular grains, or grains with irregular outline. Magnification: 40x To view this mineral in crossed polars, click here: https://youtu.be/7_4mxDpByKM To explore this slide…, Anorthite in cross polarized light. function printSpecial() F - Fit to Screen S - Stereo Pair on/off Transparent to Subtransparent to translucent. } { You can find the explanation on the plagioclase feldspar page. Mouse I - Indicies { Striated - Parallel lines on crystal surface or cleavage face. Relief: Moderate positive Habit/Form: Euhedral crystals are not uncommon, are usually tabular parallel to (001), and have a roughly hexagonal cross section. RMB - Cycle Display Modes var printReadyElem = document.getElementById("printReady"); required to differentiate them for certain. Scale: See Photo. The latter will always be much darker and more intense than thin section colours. Scanning electron micrograph of anorthite, NASA’s Astromaterials Acquisition and Curation Office, synthesis of the analyses performed on 15415. { Development Section ofthe Department ofMines, and the Geological Unit of the Atomic Energy Board, conducted a prospecting programme which included some underground development and surface diamond drilling. Twins may be wider than the twins in albite, Add tags Comment Rate. if (headTags.length > 0) Anorthite is the light mineral in this hand sample. var html = '\n\n'; Help on Above, Foit F F , Peacor D R , American Mineralogist , 58 (1973) p.665-675, The anorthite crystal structure at 410 and 830 C, T = 410 C. Ask about Anorthite here : Help on Above. Drag2 - Resize printWin.document.open(); { I - Data Info Thin sections! Labradorite (Ca %50-70 – Na %50-30) – locality in Labrador; first brought from the Isle of Paul off Labrador in about 1770. { drag2 - RMB Resize/Rotate html += headTags[0].innerHTML; Anorthite weathers quite readily, so it’s not terribly abundant on Earth. Biotite #2 thin section (hFOV 2mm) GET 360° LIVE INTERACTION. Possibly more excited than anyone has ever been about finding a plagioclase feldspar, they bagged it and brought it home. html += printReadyElem.innerHTML; PE Anorthite = 3.05 barns/electron U=PE Anorthite x rElectron Density= 8.32 barns/cc. M - Menu else Drag1 - Manipulate Crystal html += '\n\n'; if (gAutoPrint) - Start-Stop Rotation _uacct = "UA-3067463-1"; Enstatite Mg2Si2O6 °c 2001 Mineral Data Publishing, version 1.2 Crystal Data: Orthorhombic. In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). Apollo 15 astronauts David Scott and Jim Irwin collected a hand sample with an intriguing “little white corner” which turned out to be anorthite. You can find the explanation on the plagioclase feldspar page. Although some cross-hatched twinning may also occur in plagioclase, it is always very simple with only one or two cross twins per grain. Ask-A-Mineralogist from the Mineralogical Society of America Colorless, Gray, White, Red, Reddish gray. if (document.getElementById != null) The composition of plagioclase feldspar is typically indicated by the general anorthite (% An) or albite (% Ab) fraction and is easily determined by measuring the refractive index or peel angle within the crushed particles by measuring the refraction angle under a thin section. ), including thin sections, stereo views, and in situ photographs. if (document.getElementsByTagName != null) Keyboard drag1 - LMB Manipulate Structure Scanning electron micrograph of anorthite, Anorthite in plane polars Lunar Sample 15415 was interpreted to be  original moon crust and nicknamed Genesis Rock. var printWin = window.open("","printSpecial", 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes,copyhistory=yes,width=350,height=350'); A - Atoms On/Off var gAutoPrint = true; // Flag for whether or not to automatically call the print function } Home Rocks and Minerals Plagioclase Feldspar (thin section) Reference URL Share . return; Dbl Clk - Start-Stop Rotation S - Stereo Mineral Discussion Forum from Fabre Minerals - also available in but x-ray diffraction or other tests are else var headTags = document.getElementsByTagName("head"); Grains may be bent, particularly in metamorphic rocks. Bytownite (Ca %70-90 – Na %30-10) – locality at Bytown (now the city of Ottawa), Canada. P - Polyhedra On/Off } In thin section, plagioclase commonly shows the characteristic albite polysynthetic twinning. Anorthite is the calcic end member of the plagioclase feldspar series. (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. Scroll down to the bottom of the page for more, including thin section photos. Point Group: 2=m 2=m 2=m: Crystals prismatic, to 40 cm; commonly lamellar, ¯brous, or massive. B - Bonds On/Off Mindat.org's Discussion Groups Dispersion relatively weak. H - Help Screen Original Rockhounds Discussion Group Anorthite weathers quite readily, so it’s not terribly abundant on Earth. Anorthite (Ca %90-100 – Na %10-0) – from Greek for not straight, because of its triclinic symmetry. printWin.document.close(); © Jeff Weissman / Photographic Guide to Mineral Species, Mouse This prospecting established that the con-centration ofradio-active minerals, assuch, wasofno economic significance, but that the presence ofcopper minerals couldrender thedeposit … Location: Miyake-jima, Shizuoka, Japan. On the moon, however, weathering forces do not pertain; anorthite remains anorthite and constitutes much of the lunar highlands. It’s worth a read for the information, and especially for the short transcript at the beginning which captures Scott and Irwin’s giddiness at spotting the rock. This twinning is the most characteristic identifying feature of plagioclase, and makes its identification easy when present. Biotite PPL properties. Of the moon! The Lunar Science and Planetary Institute hosts dozens of images of 15415 (and other lunar samples! Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. From the Greek, an + orthos, "not upright" in allusion to the oblique crystals. Biaxial (-), a=1.572-1.576, b=1.5785-1.5832, g=1.583-1.588, bire=0.0110-0.0120, 2V(Calc)=78, 2V(Meas)=78. Español Link to . Rockhounds Discussion Group on Yahoo Groups In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). }, Jeff Weissman / Photographic Guide to Mineral Species, Monte Somma and Valle di Fassa, Italy. Apollo 15 astronauts David Scott and Jim Irwin collected a hand sample with an intriguing “little white corner.” The little white corner turned out to be anorthite, and the rock was interpreted to be a piece of the moon’s original crust. Magnification: 40x To view this mineral in plane polars, click here: https://youtu.be/OVtdk-ScaZY To explore this slide i…, Anorthite at webmineral.com Note that these are colours seen in thin-section, not hand-specimen. 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