Study Guide for Midterm Exam 1.docx

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Earth Sciences
Cristina Millan

Earth Sciences 1108 Gemstones Study Guide for Midterm Exam 1 Spring 2014 General information for the exam: a) The format of the exam will be multiple choice, true/false, and matching. b) You must bring a calculator, a ruler (optional) and a number two pencil to the exam. NO CELL PHONES!!!! c) The test will cover material discussed/shown in class, which includes: discussions in class, powerpoints, your class notes, Schumman (textbook) readings, video clips and videos shown in class, and the pertinent eReserves (pdf) readings from Hurlbut and Kammerling d) The exam will include math problems on specific gravity. Make sure the setting on your calculator is in degrees, not radians. I can help with this before the exam. The following questions are to get you thinking about the material. REMEMBER, THIS IS JUSTAGUIDE!!!! INTRO_GEMS What are gemstones  Minerals, synthetic, or organic Definition of a mineral.  Anaturally occurring, inorganic, solid constituent of the earth’s crust  Definite chemical composition and crystal structure Natural stone, vs organic, vs synthetic vs inorganic, etc….Which ones are minerals? Which ones aren’t? Why?  Synthetic: made from same material and same conditions  Crystal: mineral  Organic: comes from an organism  Inorganic: not coming from an organism List the main attributes of a material that might make it considered to be a gemstone. What makes gems desirable?  Beauty: in the eye of the beholder  Color, pattern, brilliance, sparkle, transparency, fire, luster  Rarity o Supply and demand  Value tied to fashion  High value compared to their volume and weight  Source of cash that fits in the palm of the hand  Attributes o Hardness, toughness, stability, durability All gem terminology described in Intro_Gems Outline  Variety: a modification that distinguishes itself through its look, color, or other characteristics  Mineralogy: science of minerals  Petrography: the descriptive science of rocks  Petrology: the science of the origin, history, occurrence, structure, chemical composition and classification of rocks  Species: distinguished by a specific combination of chemical compositions and crystal structure  Gem/gemstone: all have something special/something beautiful about them; most are minerals, mineral aggregates, or rocks  Stone: all solid constituents of the earth’s crust except for ice and coal  Gemology: the science of gemstones  Colored stone: all gemstones except diamonds  Rock: a natural aggregate of 2 or more minerals  Semi-precious stone: less valuable and not very hard gemstones  Imitation: resemble natural or synthetic gem material completely or partially manmade o Color, look, effect  Jewel: a piece of jewelry containing one or more gems set in precious metal  Crystal: uniform body with an ordered structure; a strict order of the smallest components in a geometrical lattice  Crystallography: science of crystals  Matrix: finer-grained ground mass than the embedded crystals  Synthesis: synthetic stone  Mineral: a naturally occurring, inorganic, solid constituent of the compositions and crystal structures Know faceted vs non-faceted gems. Know examples of both  Faceted: flat surfaces that have been cut onto stone o Brilliance  Non-faceted: o Polished  Pearls, tumbled stones o Some cut in non-planar shapes  Cabochons (flat on bottom, convex on top), cameos, intaglios (cut into stone/carved) Compare and contrast facets and crystal faces. The different parts of a faceted gem and the facet names  Stone terms o Crown: top part of the stone o Table: top facet, often largest o Girdle: edge between crown and pavilion o Pavilion: lower part of stone o Culet: small facet at bottom (the “point”) Compare and contrast intaglio, cameo, cabochon, and faceted gemstones.  Intaglio: negative image, carved into stone, non-planar  Cameo: a relief that is cut so that is raised, non-planar  Cabochon: gem cut with flat bottom surface and rounded upper surface PHYSICALPROPERTIES Know the Mohs’hardness scale, and what is differential hardness  Differential hardness: Sides can have different hardness  Hardness: resistance to scratch  1: fingernail Talc  2: fingernail Gypsum  3: copper Calcite  4: knife Fluorite  5: steel fileApatite  6: strong blade Orthoclase (feldspar)  7: strong blade Quartz  8: strong blade Topaz  9: strong blade Corundom (ruby & sapphire)  10: another diamond Diamond Know the differences between cleavage and fracture, color and luster  Cleavage: rock or mineral is weak, breakage along planes o Clean, sharp faces, shiny  Fracture: breakage along a surface but not related to its internal atomic structure o Irregular o Conchoidal fracture (glass)  Streak: color of powdered gem  Color: most unreliable property o Any color of corundum except red= sapphire o When red= ruby  Luster: how a gem appears in reflected light What is streak of a stone?  Produced by scraping across unglazed porcelain What is a carat. How is it different than a karat? What are carats used for?  Carat= weight for gemstones (200 milligrams)  Karat= unit of purity (24k gold) What is specific gravity? What and why do we use it for? How do we measure the specific gravity of a stone
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