THE MINING AND QUARRY INDUSTRY I9I4 29 



FELDSPAR 



The production of feldspar for the various uses which it serves 

 has been carried on in New York for many years. The industry, 

 however, is comparatively small, embracing four or five active 

 quarries with a combined output that has ranged recently from 

 10,000 to 25,000 tons a year. There is evidently an increasing 

 demand for the material which, in view of the abundant local sup-, 

 plies and their favorable situation with respect to the principal 

 markets, should bring the industry into greater prominence. A 

 detailed description of the feldspar deposits, both developed and 

 undeveloped, has been prepared recently by the writer and will be 

 included as a separate chapter in a report on the quarry materials 

 of New York now in press. 



The sources of feldspar are the pegmatite bodies which accom- 

 pany the crystalline formations of the Adirondacks and the south- 

 eastern Highlands. The pegmatites are abnormally coarse-grained 

 granites, consisting of feldspar, quartz and mica, with minor 

 amounts of other minerals, some of which are peculiar to this 

 association. They occur in rather limited bodies which assume the 

 shape of dikes, lenses or small bosses, intrusive in the surrounding 

 formations, and represent offshoots from a granite magma which 

 may or may not outcrop in the vicinity. The coarse grain of 

 pegmatite is its most apparent characteristic, for the different 

 ingredients assume dimensions many times larger than those 

 characteristic of ordinary granite, the feldspar being in crystals or 

 masses that range up to several feet in diameter and the quartz and 

 mica in proportionately large individuals. As a consequence, the 

 separation of the minerals can be effected usually without much 

 difficulty by means of hand cobbing in the quarry. 



The products of the pegmatite quarries include feldspar, quartz 

 and mica which are marketed separately, and unsorted crushed 

 pegmatite which recently has come into demand for various pur- 

 poses. The feldspar may belong to one of several varieties, such 

 as orthoclase and microcline which contain potash, or albite and 

 oligoclase which belong to the soda-lime series. The composition 

 of the mineral determines to some extent the uses that may be 

 made of it and should be investigated, therefore, before any deposit 

 is developed for quarry purposes. The potash varieties are the 

 ones used for pottery, for which purpose they are also required 

 to be free of iron and fairly free of intergrowth with quartz. 

 Albite is valuable for the glazing of building tile and terra cottaj 



