Optical Mineralogy Interference Figures 1 Uniaxial Figures Optical The best way to learn the optic sign of a uniaxial mineral, is to obtain an interference figure looking down, or nearly down, a crystal’s optic axis. the figure obtained is an optic axis (oa) figure; figure 5.65 shows an example. • it is possible to determine whether a uniaxial mineral is positive or negative by a simple optical test using a petrographic microscope. the procedure is as follows: • locate a crystal of the mineral that exhibits the minimum retardation • carefully focus on the crystal at using a low power objective lens • change to a high power.
Optical Mineralogy Interference Figures 1 Uniaxial Figures Optical Learn about uniaxial interference figures in optical mineralogy. this presentation covers conoscopic techniques and optical sign determination. These are distinguished from biaxial minerals by the failure of the centre of the isogyre cross to break as the stage is rotated, or if the centre of the cross is not visible, by the isogyres remaining parallel to the crosshairs. It describes how interference colors are produced when minerals are rotated to their extinction positions. it also explains different types of interference figures seen in uniaxial and biaxial minerals, including centered optic axis, acute bisectrix, and how accessory plates can determine optic sign. 3. uniaxial figures show isogyres and color rise fall regions used with a gypsum plate to determine optic sign as positive or negative. 4. biaxial figures include acute bisectrix figures and centered optic axis figures, also using gypsum plate and color patterns to determine optic sign.
Uniaxial Minerals Indicatrix Again Interference Figures Download It describes how interference colors are produced when minerals are rotated to their extinction positions. it also explains different types of interference figures seen in uniaxial and biaxial minerals, including centered optic axis, acute bisectrix, and how accessory plates can determine optic sign. 3. uniaxial figures show isogyres and color rise fall regions used with a gypsum plate to determine optic sign as positive or negative. 4. biaxial figures include acute bisectrix figures and centered optic axis figures, also using gypsum plate and color patterns to determine optic sign. The best way to learn the optic sign of a uniaxial mineral, is to obtain an interference figure looking down, or nearly down, a crystal’s optic axis. the figure obtained is an optic axis (oa) figure; figure 5.65 shows an example. Requires: conoscopic light (condenser lens in place) interference figures (viewed with bertrand lens) use of stp to determine fast and slow directions nesse, ch. 7, p. 139 143 (uniaxial) p. 143 151 (biaxial) extinction angles: where optic axis is normal to plane of thin section mineral will appear extinct for full stage rotation! applies to. Optic axis interference figure (oriented thin section): a uniaxial interference figure will consist of areas of blackness (extinction) called isogyres and of interference colors distributed along circular curves (isochromes). For a uniaxial mineral, one privileged direction always points toward the optic axis. for a biaxial mineral, the privileged directions bisect the angle between the light ray and the optic axes.
5 6 1 Uniaxial Interference Figures Geosciences Libretexts The best way to learn the optic sign of a uniaxial mineral, is to obtain an interference figure looking down, or nearly down, a crystal’s optic axis. the figure obtained is an optic axis (oa) figure; figure 5.65 shows an example. Requires: conoscopic light (condenser lens in place) interference figures (viewed with bertrand lens) use of stp to determine fast and slow directions nesse, ch. 7, p. 139 143 (uniaxial) p. 143 151 (biaxial) extinction angles: where optic axis is normal to plane of thin section mineral will appear extinct for full stage rotation! applies to. Optic axis interference figure (oriented thin section): a uniaxial interference figure will consist of areas of blackness (extinction) called isogyres and of interference colors distributed along circular curves (isochromes). For a uniaxial mineral, one privileged direction always points toward the optic axis. for a biaxial mineral, the privileged directions bisect the angle between the light ray and the optic axes.
5 6 1 Uniaxial Interference Figures Geosciences Libretexts Optic axis interference figure (oriented thin section): a uniaxial interference figure will consist of areas of blackness (extinction) called isogyres and of interference colors distributed along circular curves (isochromes). For a uniaxial mineral, one privileged direction always points toward the optic axis. for a biaxial mineral, the privileged directions bisect the angle between the light ray and the optic axes.
Solution Optical Mineralogy Lecture 8 Biaxial Interference Figures
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