7© NEW YORK STATE MUSEUM 



but in this case they may be offshoots of some buried mass that 

 were able to reach the surface on account of their more fluid condition. 



The Adirondack region is well supplied with pegmatites but they 

 are by no means equally distributed. The great anorthosite that 

 spreads over the eastern central part mainly within Essex county 

 holds no occurrences of granite pegmatite although it contains 

 abundant occurrences of coarsely crystallized labradorite feldspar. 

 The main sources of feldspar in this region are on the east, south 

 and west sides of the Adirondacks where there are many very large 

 intrusions of normal granite. The western Adirondacks, particularly 

 the section included in Jefferson, St Lawrence and northern Lewis 

 counties, is known to include numerous bathyliths and bosses of 

 granite that cover a larger portion of the surface than in any other 

 part; the granites are mainly coarse varieties, rich in quartz and 

 containing many segregated masses of pegmatite. The conditions 

 thus appear very favorable for the occurrence of extensive bodies of 

 pegmatites in that section, but the remote and inaccessible nature 

 of much of tlie area has rather discouraged exploration. 



In the Highlands region and in Westchester county pegmatites 

 are quite abundant, but only rarely reach workable dimensions. 

 The principal bodies that have been exploited up to the present 

 time occur near Bedford, Westchester county. In the central 

 Highlands there is much pegmatite and coarse granite in evidence 

 usually pinkish or grayish in color, but there are no developed 

 quarries. The pegmatites occur in considerable bodies in the 

 vicinity of some of the magnetite bodies. 



Uses of feldspar. Feldspar finds varied employment. The 

 principal outlet for high-grade potash spar is in the pottery industry 

 particularly in the manufacture of porcelain, semiporcelain, china 

 tablewares and porcelain sanitary wares and electrical supplies. 

 For such uses it is essential that the feldspar should be free of iron 

 and that it also be practically unmixed with any other minerals 

 except quartz, the presence of which is allowable up to a certain 

 extent. Anything more than a mere trace of iron serves to exclude 

 the use of spar for making high-grade pottery. The proportion of 

 feldspar used in the vitrified wares varies from lo to 35 per cent; 

 its use here is to bind together the quartz and kaolin, but it is also 

 employed in the making of the glaze when this is required. 

 Inasamuch as quartz is an essential ingredient of the pottery mix, 

 the presence of quartz in the feldspar is not in itself objectionable, 

 although some manufacturers of high-grade wares place a limit of 

 five per cent upon the aEowable free quartz. 



