Bulletin of the United States Geological Survey--Corundum and Its Occurrence and Distribution in the United States (A Revised and Enlarged Edition of Bulletin ) . 0. WASHINGTON GOVERNMENT PRINTING OFFICE 1 9 0 6 CONTENTS AND ILLUSTRATIONS. Page. Historical sketch 9 Nomenclature of cornndum 13 Physical properties of corundum 15 Crystal form . 15 Twinning .. 16 Parting 16 Fracture 18 Hardness 18 Abrasive efficiency , 18 Specific gravity 19 Optical properties 19 Chemical composition of corundum _ 20 Determination of percentage of corundum in an ore -. 21 Description of the three varieti
Bulletin of the United States Geological Survey--Corundum and Its Occurrence and Distribution in the United States (A Revised and Enlarged Edition of Bulletin ) . 0. WASHINGTON GOVERNMENT PRINTING OFFICE 1 9 0 6 CONTENTS AND ILLUSTRATIONS. Page. Historical sketch 9 Nomenclature of cornndum 13 Physical properties of corundum 15 Crystal form . 15 Twinning .. 16 Parting 16 Fracture 18 Hardness 18 Abrasive efficiency , 18 Specific gravity 19 Optical properties 19 Chemical composition of corundum _ 20 Determination of percentage of corundum in an ore -. 21 Description of the three varieties 22 Sapphire or gem corundum 22 Essential properties of a gem 22 Sapphire as a gem ... 2^ Indices of refraction of gems 28 Hardness of gems 24 Corundum 24 Block corundum 25 Crystal corundum 25 Sand corundum - _ .. 25 Emery . 26 Corundum-bearing rocks in the United States . 27 Corundum in igneous rocks 28 In peridotite . _ 28 In pyroxenite 35 In amphibolite 35 Corundum (emery) in amphibolite at Chester, Mass 38 In anorthosite 40 In norite 41 In plumasite 1 42 In andesite 44 In monchiquite 46 In granite . 48 In syenite 48 In pegmatite 49 Corundum in metamorphicbulletinofunited269prat
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