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Olaf Medenbach, Ruhr-Universitt Bochum Atlas of Optical Crystallography Olaf Medenbach Institut fr Geologie, Mineralogie und Geophysik Ruhr-Universitt Bochum 44780 Bochum, Germany olaf.medenbach@rub.de by Olaf Medenbach Interference figures, part III: dispersion and symmetry Slide 2 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m 2/m 2/m no distinctive dispersion, crystal orthorhombic, monoclinic or triclinic mirror planes m 2-fold axes Slide 3 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m 2/m 2/m, orthorhombic crystal, strong dispersion of 2V, r>>v, cerussite, PbCO 3 m mirror planes 2-fold axes Slide 4 Olaf Medenbach, Ruhr-Universitt Bochum Dispersion of 2V Why are color effects in the 45 position reverse of the true axial dispersion? Melatopes (optic axes) for blue and red light Melatopes and isogyres for blue light (points of zero retardation and extinction, respectively, for blue light), remaining wavelengths combine to red Melatopes and isogyres for red light (points of zero retardation and extinction, respectively, for red light), remaining wavelengths combine to blue Slide 5 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m 2/m 2/m orthorhombic crystal, crossed axial planes, brookite, TiO 2 m mirror planes 2-fold axes Slide 6 Olaf Medenbach, Ruhr-Universitt Bochum Dispersion of the Indicatrix in Orthorhombic Crystals crossed axial planes for blue and red light Brookite, TiO 2 optic plane for blue light: (010) uniaxial for green light optic plane for red light: (001) Slide 7 Olaf Medenbach, Ruhr-Universitt Bochum Brookite crossed axial planes for blue and red light The animation starts a few seconds after the next click. Slide 8 Olaf Medenbach, Ruhr-Universitt Bochum (010) (001) 420 nm440 nm460 nm480 nm500 nm520 nm540 nm560 nm580 nm600 nm620 nm640 nm660 nm680 nm Brookite crossed axial planes for blue and red light Slide 9 Olaf Medenbach, Ruhr-Universitt Bochum (001) (010) 420 nm440 nm460 nm480 nm500 nm520 nm540 nm560 nm580 nm600 nm620 nm640 nm660 nm680 nm Brookite crossed axial planes for blue and red light Slide 10 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m monoclinic crystal, extreme inclined dispersion 2-fold axis mirror plane Slide 11 Olaf Medenbach, Ruhr-Universitt Bochum Dispersion of the Indicatrix in Monoclinic Crystals n y = b, optic plane (010), extreme inclined dispersion, 2V v >>2V r MgPt(CN) 4 5H 2 O C 3 H 8 O 3, synthetic uniaxial for red light intermediate axial angle for green light large axial angle for blue light Slide 12 Olaf Medenbach, Ruhr-Universitt Bochum monoclinic extreme inclined dispersion The animation starts a few seconds after the next click. Slide 13 Olaf Medenbach, Ruhr-Universitt Bochum b (010) 420 nm440 nm460 nm480 nm500 nm520 nm540 nm560 nm580 nm600 nm620 nm monoclinic extreme inclined dispersion Slide 14 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m monoclinic crystal, extreme horizontal dispersion 2-fold axis mirror plane Slide 15 Olaf Medenbach, Ruhr-Universitt Bochum Dispersion of the Indicatrix in Monoclinic Crystals obtuse bisectix b, optic planes (010), extreme horizontal dispersion SrPt(CN) 4 3H 2 O, synthetic axial plane for blue light axial plane for green light axial plane for red light Slide 16 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m monoclinic crystal, extreme crossed dispersion 2-fold axis m mirror plane Slide 17 Olaf Medenbach, Ruhr-Universitt Bochum Dispersion of the Indicatrix in Monoclinic Crystals acute bisectix b, optic planes (010), extreme crossed dispersion n-propylamine picrate, synthetic axial plane for blue light axial plane for green light axial plane for red light Slide 18 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: no symmetry in the interference figure triclinic crystal Slide 19 Olaf Medenbach, Ruhr-Universitt Bochum Dispersion of the Indicatrix in Triclinic Crystals no symmetry elements present Diisopropylamine picrate, synthetic axial plane for bluegreen light axial plane for green light axial plane for red light Slide 20 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m crystal's symmetry: monoclinic diagnostic color effects m mirror plane 2-fold axis Slide 21 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m crystal's symmetry: monoclinic crossed dispersion, borax, Na 2 [B 4 O 5 (OH) 4 ] 8H 2 O diagnostic color effects 2-fold axis m mirror plane Slide 22 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m crystal ' s symmetry: monoclinic crossed dispersion, heulandite, Ca[Al 2 Si 7 O 18 ] 6H 2 O diagnostic color effects 2-fold axis m mirror plane Slide 23 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m crystal's symmetry: monoclinic inclined dispersion, high sanidine, K[AlSi 3 O 8 ] 2-fold axis mirror plane diagnostic color effects Slide 24 Olaf Medenbach, Ruhr-Universitt Bochum 2-fold axis mirror plane Find the Symmetry: symmetry of the interference figure: 2/m crystal's symmetry: monoclinic inclined dispersion Slide 25 Olaf Medenbach, Ruhr-Universitt Bochum Find the Symmetry: symmetry of the interference figure: 2/m crystal's symmetry: monoclinic horizontal dispersion, low sanidine, K[AlSi 3 O 8 ] 2-fold axis mirror plane diagnostic color effects Slide 26 Olaf Medenbach, Ruhr-Universitt Bochum Nesse (2001) after Steward & Ribbe (1983). Feldspar mineralogy, Rev. Mineral., MSA Optical behaviour of K-feldspar as a function of the degree of Si-Al order Nesse (2001) after Su et al. (1984). Am. Mineral. 69, 440-448 high sanidine: inclined dispersion microcline: horizontal dispersion (010) medium degree of order: pseudo-uniaxial