THE MINING AND QUARRY INDUSTRY I913 33 



highway leading out of Peekskill, but most have been closed either 

 on account of exhaustion or the unsuitable character of the mate- 

 rial. Some of the more extensive workings are on the farms of 

 John Buckbee and Oscar Dalton. 



FELDSPAR 



The commercial production of feldspar is based on the occur- 

 rences of pegmatite that are found within the crystalline formations 

 of the Adirondacks and southeastern New York. Pegmatite is a 

 coarsely textured variety of granite in which the individual min- 

 erals — feldspar, quartz and mica — form crystals and masses many 

 times larger than in ordinary granite. It occurs in dikes and bosses 

 intrusive in the country rocks and usually associated with large 

 bodies of granite, of which the dikes are offshoots. Such dikes 

 range from a foot or less to ioo feet thick and are often traceable 

 for long distances along the strike. The bosses appear as rounded 

 or lenticular bodies with diameters of several hundred feet in some 

 instances ; most of the workable bodies have the form of bosses 

 rather than the elongated tabular shape characteristic of dikes. 



The feldspar found in pegmatites may be one of the potash vari- 

 eties, that is, either orthoclase or microcline, or one of the soda-lime 

 species such as albite, oligoclase and andesine. Very commonly 

 both potash and soda-lime feldspar are found in the same occur- 

 rence. Microcline is by far the most frequent variety of the potash 

 feldspars in the New York localities. It is distinguished from 

 orthoclase by its striated appearance, but does not differ chemically 

 from the latter. The potash varieties are the ones commonly used 

 in pottery, but albite is preferred for some purposes as in glazing 

 of tiles and terra cotta on account of its lower temperature of fusion. 



For pottery purposes it is an advantage to have the feldspar in 

 well-segregated crystals so that it can be readily freed from the 

 accompanying minerals. The separation has to be effected by hand- 

 sorting and cobbing. In the pegmatites which are quarried for 

 pottery spar, the crystals range up to 3 or 4 feet in diameter. The 

 pegmatites of finer texture and those in which the minerals are 

 intimately intergrown have application principally for roofing 

 materials. 



Quartz is an important ingredient of all pegmatites and if ob- 

 tainable in pure condition is also of value. It is an important by- 

 product, for example, of the Kinkel quarries at Bedford. It 

 occurs in irregular masses, seldom showing any traces of crystal 



