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 metamorphic rocks 50 
In serpentine 50 
In gneiss _ . 50 
3 
