THE MINING AND QUARRY INDUSTRY 69 



The emery is composed of corundum, magnetite and hercynite 

 (iron-aluminum spinel) in varying proportions. According to the 

 investigations of Magnus, hercynite is the most prominent con- 

 stituent and constitutes in some cases 50 per cent of the mass. It 

 has a hardness of 8, as compared with 9 for corundum. The 

 magnetite forms minute inclusions in the hercynite crystals. The 

 latter have a distinct cleavage which adds to the abrasive qualities. 



The material is broken in the quarry by light charges of explosives, 

 and is then roughly cobbed and sent to the mill. As much as 100 

 tons have been taken from a single opening. The preparation at 

 the mill consists in breaking down the emery by passing through 

 crushers and rolls until of suitable size. The emery is then passed 

 through washers, after which it is dried and graded. The screens 

 used in grading range from 14 to 180 meshes to the square inch. 

 The product is employed in making emery paper and cloth and 

 emery wheels. 



The production of emery in 1905 amounted to 1475 short tons 

 valued at $12,452. A part of this quantity was held in stock at the 

 mines, the total shipments from the region being 11 58 tons. In 

 the preceding year the output was 1148 short tons valued at 

 $17,220. There were four concerns engaged in mining during 

 1905- 



Bibliography 



Magnus, Harry C. Abrasives of New York State. N Y. State Geol. 23d An. 



Rep't. 1004. 

 Nevius, J. K.' Emery Mines of Westchester county. N. Y. State Mus. 53d 



An. Rep't. 1901. 



FELDSPAR 



Feldspar suitable for pottery purposes is obtained near Bedford, 

 Westchester county. It occurs in pegmatite dikes intersecting the 

 crystalline rocks of that region and is associated with quartz, mica 

 and tourmalin. In some of the dikes the feldspar forms large 

 masses or anhedra, quite free from impurities, while in others it is 

 intergrown with quartz ; only the former occurrences, however, 

 have commercial value. The feldspar belongs to the variety known 

 as orthoclase, which is characterized by a high potash content. It 

 varies from dark red to white in color. 



The Bedford quarries have been worked since 1878. The output 

 is shipped mostly to pottery manufacturers at Trenton, N. J. 



Pegmatite dikes are an important feature of the geology of the 

 Adirondacks, being particularly abundant along the borders where 

 they are associated with Precambric gneisses. Some of the occur- 



