UNITED STATES MINERAL RESOURCES 



ABRASIVES 



By Robert E. Thaden 



CONTENTS 



Abstract of conclusions 



Introduction 



The natural abrasives _. 



Diamond 



Corundum 



Emery 



Garnet 



Silica sand 



Tripoli 



The artificial abrasives . 



Potential resources 



Selected references 



TABLE 



Page 



5. Resources of abrasive materials in the United 



States 33 



ABSTRACT OF CONCLUSIONS 



Abrasives are substances used to clean, dress, or comminute 

 other substances. They are of critical importance to the 

 economy of industrial nations. The principal natural ab- 

 rasives are diamond, corundum, emery, garnet, tripoli, and 

 silica sand, and the United States is fortunate to have iden- 

 tified resources of most of them which will serve as supply 

 at current rates of consumption for from 50 years to more 

 than 100,000 years. The United States has no commercial 

 deposits of diamond, but manufactured diamond already sat- 

 isfies more than one-half of the domestic requirements. Other 

 artificial abrasives, principally aluminum oxide, silicon car- 

 bide, and steel shot and grit, manufactured from abundant 

 raw materials, have supplanted natural abrasives in about 

 90 percent of all critical applications and, together with 

 "artificial" diamond, encroach on the few remaining uses for 

 which the natural abrasives in shortest supply once were 

 thought uniquely qualified. 



INTRODUCTION 



Abrasives are those substances that are used to 

 clean or dress the surfaces of other materials, or to 



comminute other materials by abrasion and percus- 

 sion. Because of their great diiferences in hardness, 

 abrasives have many thousands of applications. 



The deliberate removal of solid material by abra- 

 sive action consumes the bulk of all hard abrasives. 

 This includes such diverse operations as grinding 

 valve seats with abrasive-charged paste, sharpen- 

 ing tool blades with appropriately shaped abrasive 

 stone blocks, grinding and polishing bearing sur- 

 faces on machine components with bonded granu- 

 lar abrasive wheels, sandblasting inscriptions on 

 tombstones, and slabbing and drilling rock with 

 abrasive-charged discs, wires, and drill bits. 



The cleaning function employs abrasives softer 

 than the material being cleaned to remove a sur- 

 face film of foreign material with minimal damage, 

 as in brushing the teeth with dentifrice, or in scour- 

 ing porcelain bathroom fixtures or automobile paint 

 with abrasive soap. 



Comminution can be effected by heavy abrasive 

 wheels or by abrasive pebbles tumbling or cascad- 

 ing in a mill. By the latter process, ores, for ex- 

 ample, are reduced to the size required for their 

 further metallurgical treatment, small parts are 

 deburred, wheat is ground to flour, and talc and 

 paint pigments are ground to the size appropriate 

 for their ultimate use. 



Strictly speaking, neither sandblasting nor the 

 crushing of ore by cascading pebbles of shot are 

 abrasive operations, inasmuch as the action is one 

 of percussion. Nevertheless, these processes are in- 

 cluded here not only because both the "abrasive" 

 materials and the effects are the same as though 

 the operations had been accomplished by abrasive 

 action, but because historically the abrasives used 

 in percussive applications have not been differen- 

 tiated in tables of production statistics from the 

 same materials used for true abrasive purposes. 



The first applications of loose grains of quartz and 

 of quartz sandstone and other naturally bonded 



U.S. GEOL. SURVEY PROF. PAPER 820 



27 



