MINERAL RESOURCES OF THE STATE OF NEW YORK 15I 



article by Sterrett in Mineral Resources for 1912, voliime 2, there 

 are probably as many as a hundred separate mines and prospects, 

 many worked by farmers in the off-season of their labors. As the 

 entire output of the country in recent years has been well under 

 $400,000 annually, the average outturn from the individual mines 

 evidently is very small. India contributes most of the mica con- 

 sumed in the United States, though Canada is an important source 

 of the electrical grades. It has been stated (Mineral Industry for 

 19 1 2) that the cost of labor in the production of mica in India is 

 about one-sixth of the labor cost in the domestic mines. 



The quality of mica depends upon a great many factors which 

 can be estimated accurately only by the expert. Of the three vari- 

 eties, biotite has more limited use than the others and the market 

 does not warrant mining operations for its production alone. It is 

 obtained mainly as a by-product in the working of pegmatites for 

 feldspar. Owing to its iron content it is not much used for electrical 

 insulation, which is the principal application for the colored micas. 

 Muscovite, having the greatest transparency, is preferred for glazing 

 and for lamp chimneys, shades and similar purposes. The larger 

 sizes only can thus be used. For electrical insulation in motors 

 and dynamos, phlogopite seems to find the most favor, on account 

 of the softer nature of that variety, it is said. Much of the electrical 

 mica is used in the form of " micanite," which consists of small 

 sheets cemented and compressed into boards. The presence of 

 inclusions of iron oxid, usually magnetite, which is quite common 

 in muscovite and phlogopite, is stated by Sterrett to have no injurious 

 effect upon the quality of the electrical mica. 



Much of the mica as found in pegmatites and contact zones, even 

 when in large crystals, can not be used in sheet form on account of 

 the numerous fractures and lines that traverse the surfaces. There 

 is great variation in the splitting quality of mica from different 

 places, some examples cleaving readily and cleanly even to very 

 thin sheets and others showing a splintery surface. The average 

 size of sheet that can be obtained largely determines the value 

 of a deposit, since the prices rapidly decrease with the size. The 

 waste in the splitting is sometimes turned into use by converting 

 it into ground mica for which there exists a more or less ready 

 market in the making of lustrous coated papers, lubricants and 

 insulating materials. 



Field Occurrence 



Orange county. Phlogopite of greenish color is found in a pyrox- 

 ene rock near Lake Mombasha, town of Monroe. The locality 



