Quiz 2 review.docx

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University of British Columbia
Earth and Ocean Sciences
EOSC 118
David Turner

Quiz 2 review COLLAPSE Hi Class! Good work on Quiz 2! The average on the quiz was ~16.1, and the following questions were some of the most commonly mis-answered. Please use these to help refine your learning, and please post any other questions you might have here! Remember also that we only take the top 3 of 4 quizzes in calculating your final course grade. Dave, Jan, Dana and Martyn Mineralogy Q: Total internal reflection contributes to the brilliance of a gemstone by: A: … returning light that enters through the crown and table of a gemstone back to our eyes. Q: Anisotropic minerals have: A: …more than one refractive index along the crystallographic directions. The crystal system of a mineral will define whether it is anisotropic or isotropic. An anisotropic mineral can have either 2 or 3 distinct refractive indices, but they don’t necessarily need to be very different. The monoclinic, orthorhombic and triclinic systems have 3 refractive indices. The tetragonal and hexagonal systems have 2 refractive indices. Examples of anisotropic minerals include quartz, corundum, beryl, tanzanite, etc... Isotropic minerals belong to the cubic/isometric crystal system and have only 1 refractive index, with important examples being diamond or garnet. This is important for identification of gemstones, since identification of this property can rule out large swaths of potential minerals. For example, moissanite is a diamond imitation (and a good one!) but it has a hexagonal crystal system and is therefore anisotropic whereas diamond has a cubic crystal system. Q: Fluorescent lighting is can be problematic for selling items for which colour is a selling factor, including gems, because: A: the bulbs emit light irregularly across the spectrum, with spiked emittance at several short wavelength segments, especially violet and green Q: Internal reflection … A: … is sought after when cutting diamonds and occurs when much of the light that enters a cut gem is returned through the table to your eye. Q: A translucent specimen ______. A: … transmits less light than semi-transparent specimens. This one can be rather intuitive – if you can look through the material (semi-transparent), it must transmit more light than if you can only see that some light passes through (translucent). BERYL Q: Which statement is true: There are no more emerald deposits to be found, because every likely spot where the geological environment is correct has already been checked. – Not true, since we currently have an information on bedrock from a small part of Earth’s surface only (it is often covered by glacial sediments or other sedimentary rocks, swamps, lakes, soil, etc.) and from a very tiny part of Earth’s crust interior (which we can study in detail only in drill-cores or in underground mines). Research on emeralds is always ongoing, but is hampered somewhat by the fact that Be is notoriously difficult to analyze in a lab environment. – True. Beryl grows best in high-pressure environments like the lower crust, where the crystal is tightly packed on all sides during growth. – Not true, beryl forms in or around granitic rocks or in hydrothermal system in low-pressureenvironments in upper part of Earth’s crust. Emerald deposits are easy to find because the two necessary geologic conditions for most deposits, mafic rocks and felsic magmas, are always found together in the same location. – Not true, these two rock types do not always occur next to each other. New deposits of highest-quality eme
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