ABRASIVE HATERIALS. 



BY JOSEPH HYDE PRATT. 



[Joseph Hyde Pratt, geologist and consulting mining engineer; bom Hartford, Conn., 

 February 3, 1870; graduated from the Sheffield Scientific school of Yale university; 

 instructor in mineralogy at Yale and later at the University of North Carolina; state 

 geologist of North Carolina, 1897-99; assistant geologist of the United States geologi- 

 cal survey since 1900. Author of about 125 monographs and other articles on miner- 

 alogy and geology, mostly contributed to scientific periodicals.] 



The natural abrasive materials can readily be divided 

 into two general groups: 1. Those which occur as rock for- 

 mation and are cut and manufactured directly into, the form 

 desired, while retaining their original rock structure and ap- 

 pearance, as grindstones and whetstones. 2. Those which 

 occur as a constituent of either a rock or a vein, and have to 

 be mechanically separated from the associated gangue and 

 cleaned, as corundum, emery, and garnet. 



The artificial products would make a third class of abra- 

 sive materials, including carborundum, crushed steel, etc. 

 The abrasive materials are so universally distributed 

 that there are but few localities where some of them may not 

 be found. While this is the case, various kinds of abrasives 

 are constantly being exported from and imported into the 

 different countries on account either of their superior abrasive 

 efficiency or of their better adaptability to required purposes. 



The use of any particular abrasive is dependent upon the 

 character of the abrasion to be accomphshed. Thus while 

 the efficiency of a certain abrasive, as an abrasive, may be 

 greater than that of another, it will not do as satisfactory 

 work as one with less abrasive efficiency. For instance, al- 

 though corundum has the highest abrasive efficiency of any 

 included in the second type of abrasives mentioned, there are 

 a number of cases where garnet, with a much lower abrasive 

 efficiency, will give better satisfaction. 



The abrasive that is perhaps the most familiar to all is 

 the grindstone. This is produced at the present time in com- 

 mercial quantities in Michigan, Ohio, and West Virginia, and 

 in much smaller quantities m Montana and Wyoming. The 



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