THE MINING AND QUARRY INDUSTRY IQII 23 



The corundum, which is the most valuable constituent from the 

 abrasive standpoint, may constitute as much as 50 per cent of the 

 entire rock, and in the typical material is often seen in the form of 

 large porphyritic crystals scattered through a fine-grained mass of 

 magnetite and spinel. The rock is dense and hard, of dark gray 

 to nearly black color, sometimes mottled by the lighter crystals of 

 corundum. It occurs as lenticular and banded masses within local 

 intrusions of basic gabbroic rocks which are known as the Cort- 

 landt series. The emery masses are believed to represent segrega- 

 tions of the heavier minerals of the gabbro while the latter were 

 in a molten condition, a process similar to that which led to the 

 formation of the titaniferous magnetites in the anorthosites and 

 gabbros of the Adirondacks. Some of the deposits in Westchester 

 county contain a fairly high percentage of magnetite and were 

 once mined for iron ore, but owing to the high alumina content 

 proved too refractory for furnace use. 



The output of emery last year was below the usual average, 

 showing a decline of about 200 tons from the total reported in 

 1910. The actual amount reported by the producers was 769 short 

 tons with a value of $8810. In 1910 it was 978 short tons valued 

 at $11,736. The maximum product for any recent year has been 

 about 1500 tons. 



The emery is all shipped in lump form to abrasive manufac- 

 turers, who grind and prepare it for use. The list of producers in 

 1911 included the Blue Corundum Mining Co., Easton, Pa.; Key- 

 stone Emery Mills, Frankford, Pa. ; and John Buckbee, Peekskill. 

 In former years the Hampden Corundum Wheel Co. and 

 R. Lancaster have been active in the district. 



FELDSPAR 

 The commercial grades of feldspar are obtained in this State 

 from pegmatite bodies that accompany the crystalline formations 

 of the Adirondacks and the southeastern Highlands. The pegma- 

 tite has the composition of granite and represents a coarse phase 

 of that rock originating through specially favorable conditions of 

 crystalHzation supplied, perhaps, by abundance of water vapor. It 

 is commonly associated with granites and granitic gneisses, but may 

 be found as offshoots or independent bodies surrounded by rocks 

 of quite different character. In the granite areas it occurs fre- 

 quently in lenticular and irregular masses which show no distinct 

 boundaries but grade by imperceptible stages into the finer-grained 



