MINERALS AND GEMS
MINERALS AND GEMS ESS 103
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This 3 page Class Notes was uploaded by Miss Jeanette Keebler on Wednesday September 9, 2015. The Class Notes belongs to ESS 103 at University of Washington taught by Michael Harrell in Fall. Since its upload, it has received 38 views. For similar materials see /class/192655/ess-103-university-of-washington in Earth And Space Sciences at University of Washington.
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Date Created: 09/09/15
ESS 103 lecture notes introduction Reading Assignment Back of syllabus subject to modi cation Note that J Johnsen S Schumann Don t be alarmed by lengthy readings These are ID manuals not texts so it isn39t as bad as it looks Lecture quotMineralquot and quotGemquot not synonymous but much overlap Most minerals are not gems but most gems are minerals Mineral is essentially a scienti c term gem is essentially an aesthetic term NOT economic by the way as either group can be pro table quotOrequot is economic term De nition of amineral l Naturally occurring Contrast with synthetic mat ls emphasize desire to interpret geologic conditions 2 Inorganic Organic processes considered separately Again for interpretation 3 Solid strict sense means crystalline 4 Speci c structure at atomic scale crystal structure eg regular periodic pattern ordered atomic arrangement 5 Speci c or limited range of chemical composition Homogeneous unifonn throughout more or less Examples Salt yes Sugar no Cubic Zirconia no Glass no Ice yes Explain why Implications of de nition Many minerals book says c 2500 now over 3000 Most are ah obscure Diagnostic physical properties exist are useful for identifying minerals A given mineral only forms under certain P T X conditions Can deduce conditions under which it formed Immensely useful in geology Mineraloids quotAlmost but not quitequot Meet all the parts of the definition except one usually are not crystalline Glass resin opal Some gems are this Will return to this Definition of a gem Minerals and some nonminerals of ornamental value About 20 minerals give rise to about 30 common gems As you ll see in Schumann several more minor gems also exist 1 Beauty Subjective but generally agreed that some are more pleasing than others 2 Durability Must stand up to use hold its shape whether natural or cut Rule of thumb no softer than quartz Some uses for softer stuff but not for wearing 3 Rarity Not too rare since must be able to sustain widespread interest Unlikely that new gems will be discovered Some common minerals such as quartz or corundum are gems when the occur in a rare form or color amethyst ruby sapphire Will focus first on minerals emphasis on gem minerals Forms basis for understanding the rest What is so fascinating about minerals One obvious feature is they often are found with at faces at fixed angles to one another forming regular geometric shapes Nicolaus Steno s drawings from mid1600s Different sizes of faces same angles Unfinished dissertation actually this was only a side point but now viewed as a significant insight in and of itself Not always the case as you ll find in lab Perfect specimens usually rare This looks pretty neat even today but imagine how noticeable it was in the past before modern manufacturing techniques when it took a great deal of effort to make something at and true with sharp edges Here it was occurring on something pulled out of the ground How to make minerals One idea from Hauy late 1700s was that building blocks of different shapes were responsible since they would stack in a certain way Here for the mineral garnet little cubes stack to form either a cube or by forming pyramids on each side of the cube a dodecahedron Not too different from modern idea regular threedimensional stacking of atoms Can look at how the atoms bond to one another draw imaginary box around them Box is called a UNIT CELL Stack unit cells together to form the CRYSTAL LATTICE Can assign coordinates delve into geometry Won39t do that here but will cover some of the different types of unit cells and the different crystal symmetries that result next time Note that the assigned reading on crystal symmetry goes into much greater detail than we will cover in the labs or lectures I will not include this additional material on the exams but you may find it useful for mineral identification
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