one week of notes
one week of notes GEOL 3372
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This 2 page Class Notes was uploaded by Valeska Guzmán on Thursday January 21, 2016. The Class Notes belongs to GEOL 3372 at University of Houston taught by Peter Copeland in Spring 2016. Since its upload, it has received 21 views. For similar materials see Petrography in Natural Sciences at University of Houston.
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Date Created: 01/21/16
All about the slides, knowing without the book. How to use a microscope, why use it, to identify minerals in hand specimens in the field is not easy is easier in thin section. Look at color, cleavages, and angles from that you can determine rock type. It tell you a lot about the history looking at the deformation patterns, looking at reactions tell you history. For sedimentary you can tell what kind of rocks were deposited, whether this rocks have been weathered. These machines can tell you a lot: Polar petrographic microscope: this device polarizes the light, stage rotates 360. A rock is cut to be glued to the slide and thinned until almost gone. Thickness about 300 of mm light passes through 2 ndpolarizes which polarizes the light it polarizes at right angles looking at plain light (PPL), crossed polarized (XN) once called nicols prism. Physics of light- light vibrates and has a source different wavelengths= different colors. Some biotites have properties better than color light travels in waves. We are not describing light as particles. Light at bottom of microscope is white we can break this with a prism, creates different number of waves, we want to polarize light to distribute light. If something is vibrating slightly off you can divide vectors then add second polarizer--- black. When we out a sample you get an image the main conclusion is minerals change the light is the rock that did that creates different colors and have different properties. Nicols polarizer, cross nicols= both polars. Some minerals always black. Natural glass vs mineral= structure and crystallization Mineral=natural occurring, chemical composition glass doesn’t have internal structure, structure identical in every direction, is an isotropic behavior of light. Anisostrophic = mineral grain changes the light breaks it up into 2 phase, different in speed, change in orientation Birefringence or interference of colors= thin section They have different velocities and have certain orientations Optic= which orientation of fast and slow rays color=only plain light Some minerals like hornblende and tourmenaline pleochroism= changes color as you spin it around of same mineral Mineral property=bending of ight relief= 2 adjacent grains Olivine appears higher n=ratio of velocity of light Composition of olivine can change that is why it gets a range of different orientations Epoxy= brings together rock and glass changes in reflective index - N Higher-n lower = difference Thickness in thin section shows more retardation between rays Everything about the mineral affects velocities. When large .03 we will see colors Uniaxial vs biaxial
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