THE MINING 



AND QUARRY INDUSTRY 



71 



and iron. It has a hardness ranging from 7.5 to 8, above the aver- 

 age for this mineral, and is thus intermediate between quartz (7) 

 and corundum (9). For some purposes the Adirondack garnet is 

 even preferred to corundum, though the latter commands a higher 

 price in the market. 



The deposits at present worked are found in Warren and Essex 

 counties near the upper Hudson valley. North Creek, the terminus 

 of the Adirondack branch of the Delaware & Hudson railroad, is 

 the principal point of shipment. The mines are situated north and 

 west of this locality within an area 10 or 12 miles long extending 

 north from Gore mountain. 



The garnet is usually associated with a basic hornblende rock 

 or amphibolite which forms bands and lenses in the more acid gneiss 

 that constitutes the country rock of this region. The amphibolite 

 shows evidences of metamorphism which has brought about a re- 

 crystallization of its minerals and has probably led to the formation 

 of the garnet. The latter occurs in crystals, ranging from an inch 

 or less up to several feet in diameter. It has a deep reddish color. 

 The larger individuals seldom show crystal boundaries and are so 

 shattered that they readily crumble into small fragments. They 

 usually contain a small proportion of quartz, mica and other minerals 

 that have been included during crystallization. 



Ordinary quarry methods are used in working the deposits. The 

 rock is broken down by pick or by blasting and the garnet recovered 

 by hand sorting or mechanically. The North River Garnet Co. 

 has the only plant for mechanical treatment of the rock, which con- 

 sists in passing it through crushers and concentrating on special 

 types of jigs. The separation is a matter of some difficulty as the 

 garnet and the accompanying hornblende differ but little in specific 

 gravity. The process developed by this company has been, how- 

 ever, very successful. 



Most of the output of garnet is consumed in the shoe and wood- 

 working industries, for which purposes it is graded into various 

 sizes and made into garnet paper. Although garnet does not possess 

 the property of cleavage, there is a tendency to parallel parting 

 which is very marked in the Adirondack mineral. This is of great 

 advantage to the use of garnet as an abrasive, as it gives a smooth 

 surface for attachment to the paper and also insures a sharp cutting 

 e*dge. The efficiency -of garnet paper under the usual conditions is 

 stated to be several times greater than the best sandpaper. Inferior 

 grades of garnet mixed with emery or corundum have been employed 

 in making abrasive wheels. 



