Gemstones Week of 4 6
Gemstones Week of 4 6 1108
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This 3 page Class Notes was uploaded by Caroline Bacevice on Thursday April 9, 2015. The Class Notes belongs to 1108 at Ohio State University taught by Loren Babcock in Spring2015. Since its upload, it has received 39 views. For similar materials see Gemstones in Earth Sciences at Ohio State University.
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Date Created: 04/09/15
Gemstones Week of 4 6 Radioactive Dosage Zircon 1 nanoCurie nCi gram g of U238 o nCi billionth of a Curie Irradiated Blue topaz 25 nCi g The average human body contains 200 nCi of radioactive potassium K40 The average human body consumes 14O nCi of K40 per year Radioactivity dosage from gems is insignificant WHAT IS A CURIE Treatment of Zircon Crystals that have become cloudy due to radioactive decay Metamict crystals can be restored by heat treatment 1450 Celsius Heating of brown Zircon 8001000 Celsius o In reducing environment Produces colorless or blue zircon o In air produces colorless or yellow zircon Most colorless or blue stones have been heat treated often brilliant cut to resemble diamonds o Distinguished from diamonds by double refraction Heating makes zircon more brittle and faces abrade more easily Chrysoberyl From Greek chrysos golden and beryllos referring to beryl Golden beryl is a misnomer Alexandrite variety showing color change in different types of light Named for Czar Alexander 11 of Russia Cymophane From Greek cymos waving and phanos light Chrysoberyl Characteristics Composition Beryllium aluminum oxide BeAlZO4 Hardness 85 Colors Yellow greenyellow green brownish red light blue Streak White SG 373 RI175176 Crystals Orthorhombic Luster Vitreous Origins Occurs in igneous rocks granites pegmatites and metamorphic rocks mica schists Also occurs in alluvial deposits in Sri Lanka Brazil China India Alexandrite Discovered in the Ural Mountains Russia in 1833 Now found in gem gravels of Sri Lanka mined in Zimbabwe Brazil Myanmar Zambia India Synthesized by ame fusion Czochralski processes Much labcreated alexandrite is berylliumOdoped corundum sapphire Chatoyancy Chatoyancy Silky sheen resulting from closely packed parallel fibers or parallel needlelike inclusions CAT S EYE EFFECT Produces cat s eye effect when stones are cut en cabochon rounded Chatoyancy is present in various minerals chrysoberyl quarts etc o Chatoyant chrysoberyl is sometimes called cymophane o Tiger s Eye quarts replacement of fibrous crocidolite asbestos Spinel From latin spina little thorn referring to sharp points on octahedral crystals Redspinel has often been confused with ruby 0 Many historic quotrubiesquot were probably spinel Composition Magnesiuk aluminum xide MgAlZ O4 Hardness 8 Color Collerless Red Orange Yellow Green Blue Indigo Violet Streak White SC 360 RI 172 Crystals Cubic often octahedrons Luster Vitreous Igneous and metamorphic mineral Gem gravels of Burma Sri Lanka Thailand associated with corundum Synthesized by ame fusion Verneuil method Often used as a cap on doublets or triplets Famous Spinel Black Prince s Ruby In the English Imperial Crown of State 0 Once thought to be a ruby o Specimen is 5 cm long uncut just polished Quartz Transparent Varieties Rock Crystal Colorless Amethyst Purple Citrine Yellow Smoky quarts brown gray or black Rose quartz Pine Ametrine Colorzoned amethyst citrine Rutilated quartz Colorless usually with inclusions of rutile needles Prase prasiolite Leekgreen Translucent to opaque varieties Various forms of cryptocrystalline and fine grained quartz including o Chalcedony including agate 0 Flint or chert Quartz Origin and history of some names Quartz From German quartz originally applied to massive vein quartz applied to all varieties by the end of 18th century Rock crystal from Greek krystallos ice Amethyst From Greek amethystos not to intoxicate ancient belief was that wine drunk from an amethyst cup would not cause intoxication Citrine From old French Citron yellow Chalcedony Possibly from Chalcedon an ancient seaport in Asia Minor Carnelian From Latin carnis esh referring to the red color Prase From Greek prason leek in allusion to its green color Characteristics Origin Composition Silicon Dioxide SiOZ Hardness 7 Colors ROYGBIV Streak White except for Tiger s Eye which is yellowbrown Specific Gravity 266 Crystals Hexagonal trigonal Luster Vitreous Cleavage None breaks by conchoidal fracture that looks like a shell Common in most igneous sedimentary and metamorphic rocks Quartz is quite resistant to mechanical abrasion it is the most abundant mineral following weathering and erosion 0 Common in stream sediments on beaches in wind blown deposits Synthetic quartz First synthesized in the 1800s by the hydrothermal method