Gemstones week of 2/9
Gemstones week of 2/9 1108
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This 2 page Class Notes was uploaded by Caroline Bacevice on Thursday February 12, 2015. The Class Notes belongs to 1108 at Ohio State University taught by Loren Babcock in Spring2015. Since its upload, it has received 64 views. For similar materials see Gemstones in Earth Sciences at Ohio State University.
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Date Created: 02/12/15
Gemstones Week of 29 Observations on cut and uncut gemstones Color Fluorescence Luster Specific gravity Refractive index finger print of the gemstone Dispersion Various phenomena cat s eye effect star effect etc Optical properties Heat and electrical conductivity Diamonds and Diamond Simulants Chapter 4 Diamond Origin of name and early legend From Old French diamant after Greek and Latin adamas meaning invincible or unconquerable Originally adamas ususally referred to iron or iron alloy About 50 AD Ovid uses adamas in the sense of a diamond Be 70 AD Pliny the Elder described diamond testingquot Diamond resisted the blow of an iron hammer quotMNot true Many Diamonds were shattered by minders in India and South Africa Characteristics Composition Pure Carbon C Hardness 10 Streak White Specific gravity 352 Refraction Index 242 dispersion 0044 Crystals cubic system often octahedrons or cubes Luster Adamanite Formation of Diamonds From near the coremantle boundary 0 Depth 2900 km 1800 miles 0 High pressure conditions 9001300 degrees C 45 to 60 kilobars Diamonds are carried to the surface as inclusions in pipes of volcanic rock and erupted o Kimberlite or lamproite peridotite an ultramafic rock Diamond ages most are gt990 million years many are 32 billion years old Graphite not diamond is the stable form of Carbon at the Earth s surface 0 Diamond will burn or oxidize on the surface if dropped in a fire for a short time o If heated to bright red a diamond will catch fire and convert to C02 gas To avoid conversion to graphite diamonds must rise to the surface rapidly I Probably travel 10 to 30 km hour part of the way I Near the surface the transport rate probably increases to several hundred km hour I Time needed to reach the surface lt12 hours Why are Diamonds so hard And why is graphite not Both are polymorphs of Carbons Diamond Atoms are linked in a 3D network Graphite Atoms are linked in sheets 0 Little holds the sheets together so they easily slide past one another making the mineral soft Where were diamonds collected so early in history Ancient times to at least 800 BC all diamonds came from alluvial gravels in India eroded from kimberlite piped in the Golconda area 1725 Diamonds were discovered in alluvial gravels of Brazil Continues to be major source of diamonds today The South African diamond rush 1859 Diamonds discovered in alluvial gravel rivers of South Africa 1867 First authenticated find 1870 Diamonds discovered in kimberlite pipes blue groundquot or yellow groundquot if weathered near Kimberly 1871 Diamonds discovered on the de Beers farm resulting in a large mine called the Big Holequot