THE MINING AND QUARRY INDUSTRY 1913 ^5 



likelihood that it will be displaced in the trade by other abrasive 

 materials. But the market is not capable of absorbing more than 

 a few thousand tons a year, at least on the present basis of prices. 

 The production in New York State for many years has ranged 

 between 4000 and 5000 short tons, the largest recent output having 

 been in 1907 when it amounted to 5709 short tons, and the average 

 selling prices have remained steady at around $30 to $32 a ton 

 for the standard grades of crystallized garnet. 



The important qualities of abrasive garnet seem to be those of 

 hardness, toughness and cleavage. In hardness, the different garnet 

 species vary considerably, and most of the garnet that is mined for 

 abrasive uses is almandite (iron-alumina garnet) which has a hard- 

 ness of 7 — 7.5 on the mineral scale, or between that of quartz and 

 topaz. Well-crystallized material which is relatively free of im- 

 purities has greater strength and stands up better under conditions 

 of service than the finely granular mineral or that containing in- 

 clusions of other minerals. The common impurities of garnet are 

 chlorite, mica, hornblende and pyroxene. It is an advantage, also, 

 if the garnet possesses a parting or imperfect cleavage so that it 

 breaks with one or more plane surfaces. Much of the Adirondack 

 garnet shows a well-developed parting, and the faces often present 

 a sharp chisel-edge that is not usual in any other natural abrasive. 

 Color, of course, is not a criterion of value, but abrasive manu- 

 facturers express a preference for the darker shades which in the 

 crushed product appear almost a ruby red. The garnet crystals 

 should also be sufficiently large so that when they are freed from 

 their matrix by crushing or other means, they will afford a desirable 

 assortment of sizes. The normal result of milling operations is to 

 produce an excess of the finer sizes. 



Notwithstanding the wide distribution of garnet as a common 

 component of the metamorphic rocks, especially the gneisses and 

 schists, there appear to be few localities where the material has 

 the essential qualities and occurs in sufficient quantity to be com- 

 mercially valuable. In this country the most productive deposits 

 are found in the Adirondacks. North Carolina and New Hamp- 

 shire have supplied small quantities in recent years, and there are 

 mines, now inactive, in Maine, Massachusetts, Connecticut and 

 Pennsylvania. A description of the local deposits and the methods 

 employed in their exploitation will be found in earlier issues of 

 this report. 



