stones Week of April 20
stones Week of April 20 1108
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This 5 page Class Notes was uploaded by Caroline Bacevice on Thursday April 23, 2015. The Class Notes belongs to 1108 at Ohio State University taught by Loren Babcock in Spring2015. Since its upload, it has received 77 views. For similar materials see Gemstones in Earth Sciences at Ohio State University.
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Date Created: 04/23/15
Gemstones Week of April 20 Tourmaline Group Tourmaline From Sinhalese turmali stone with mixed colors Shown well in bicolor tourmaline or watermelon tourmaline color zoned pink center and green rim Occurs in igneous rocks especially pegmatites metamorphic rocks and gem gravels Tourmaline Characteristics Composition Complex borosilicate May contain Na Al Ca Li Fe Mn F BO33Si6018 Solid Solution Series Hardness 775 Colors Wide Range Streak White SG 306 RI 162164 Crystals Hexagonal Luster Vitreous Garnet Group Garnet From Latin granatus grain Pyrope red From Greek pyros fiery Tsavorite green grossular From Tsavo National Park Kenya Occurs in igneous metamorphic and sedimentary rocks Also in alluvial deposit Found Worldwide Garnet Characteristics Composition Aluminum or magnesium silicates of various compositions Hardness 6575 Colors Wide range Streak White SG 315430 RI 172189 Crystals Cubic Luster Vitreous in most adamantine in demantoid garnet Lapis Lazuli Origin of name From Persian Iazhward blue Composition A rock not mineral composed of lazurite calcite pyrite commonly sodalite and other minerals Origin metamorphic Color Blue mixed with white and brassy speckles Turquoise Origin of name From French turquoise Turkish Turkish Stone because the trade route that brought the gem to Europe passed through Turkey Composition Hydrated copper aluminum phosphate Origin Fills fissures in weathered volcanic rocks Colors Medium blue greenishblue green Gold Silver Platinum precious metals Each is a native element Opaque Soft harness 253 gold silver 4 55 platinum Streak color of the metal Gold gold silver silverwhite platinum gray to white Heavy Specific Gravity 10Silver 19Gold 21 Platinum Luster Metallic Other characteristics ductile malleable conduct heat electricity Au Symbol for Latin work aurum Silver Symbol from Latin argentum Distinguished characteristics develops a gray to black tarnish Both occur in hydrothermal veins commonly with quartz pyrite etc Second source Placer deposits akes nuggets Pyrite Fool s Gold Distinguished by 0 Greater hardness o Brownish black or greenish black streak Brassy mineral disseminated in lapis lazuli Platinum From Spanish platina silverlike Distinguishing Characteristics contains up to 28 iron distinctly magnetic Alloys Precious metals in the pure state are soft To increase hardness and durability alloys mixtures of the metals are used Alloys can be used to change the color of gold white rose green Gold Alloys 0 Karat K or KT Amount of pure gold present in the alloy American usage 0 Maximum 24K 0 European marking based on portions of 1000 parts pure gold1000 Other Markings Gold Plate marked GP EP Thin layer of gold electroplated to surface of a base metal 0 Gold is easily worn off because it is only a few microns thick Sterling Silver 925 pure silver 925 sterling Silver Plating Silver electroplated over another metal alloy Platinum usually marked as PLAT or 950 What are the organic gems Pearls Characteristics Composition Calcium carbonate CaCO3 conchiolin organic binding agent water Hardness 35 Colors Various Luster Pearly Other characteristics Iridescent orient Fluorescence often pale green or reddish Pearl Origin Formed by mollusks clams especially oysters snails Pearl oysters secrete alternating layers of aragonite CaCO3 86 and conchiolin organic 10 Concentric mineral layers are deposited around an irritant o Parasite or other irritant Iridescence orient of pearls is due to overlapping plates of nacre mother of pearl Nacre Alternating layers of aragonite and conchiolin Cultured Pearls A small bead of shell is wrapped in a piece of mantle tissue Bead is inserted into the oyster next to inner side of shell 0 Bead irritates oyster o Oyster deposits nacre over it Oysters are returned to the water in cages and harvested after a couple of years 0 2 years needed to deposit 1 mm layer of nacre Pearl Valuation Valued according to shape color size surface condition and luster Nearly spherical large nearly awless and lustrous pearls are more highly valued Baroque pearls pearls having unusual shapes 0 Example Hope Pearl owned by Lord Hope same as Hope diamond History of Pearls Used as gems for gt6000 years Pearl trade in China by 2500 BC Cultured Pearls produced in China by the 1200s Round cultured pearls first produced by Carl von Linne Carolus Linnaeus in 1761 in river mussels of Sweden Kokichi Mikimoto first produced cultured pearls on a large commercial scale in 192 1 Simulants glass plastic Amber Origin Hardened tree resin in sedimentary deposits Resins are produced by conifer trees as a defense against insects and disease Amber Fossil resin gt11700 to million years old Copal Subfossil Resin Amber Characteristics Composition mix of organic resins Hardness 225 Colors mostly yellow brown sometimes greenish Streak white SC 108 Floats in salt water RI 154 SR Luster Vireous to resinous polished Other characteristics Amorphous Inclusions are common Occurence of Amber Largest deposit blue clay near Kaliningrad Russia Baltic Sea area washes up onto shore Collected as far away as Dominican Republic Historical Uses of Amber Used for adornment since at least the Paleolithic age Used for jewelry and artwork by ancience Greeks Romans and Egyptians Used in Europe during Middle Ages for religious objects and Secular art Ancient Egypt resins used as a base for paint Varnish and lacquer have long been produced from ground resins Shell essentially same as Pearl Origin Aqueous mollusks Composition Calcium carbonate Oldest known jewelry pierced snail shells 82000 years old from Morocco Iet Origin Skeletons of marine corals tropical seas Composition Aragonite Hardness 34 Colors Various Streak White Luster Vitreous polished Origin Elephant Tusk mammoth tusk walrus tusk etc Composition Calcium Phosphate Hardness 23 Color White cream Streak white Luster Pearly Origin Bituminous coal sedimentary deposits worldwide but mostly from England Composition Carbon Hardness 254 Colors Black dark brown Streak Black Natural and Imitation jet 0 Whitby jet natural coal 0 French jet black glass What is a fossil Any evidence of ancient life 0 At least 11700 years old Petrified Wood Wood fossilized with silica chalcedony or opal Dinosaur Bone Dinosaur bones with pore spaces filled with silica Luster Vitreous to pearly Mesozoic
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