THE MINING AND QUARRY INDUSTRY I912 2J 



employed as a surface coating with tar or some bituminous binder. 

 The spar is crushed to pea size or a little coarser and by reason of 

 its good cleavage yields flat surfaces that are of advantage in secur- 

 ing firm adherence. The purity of the material, however, is a 

 subordinate factor; the pegmatite which contains more or less 

 quartz, mica and other minerals, is crushed down to size just as 

 it comes from the quarry. Besides the roofing grades, there is 

 more or less fine material resulting from the crushing, which is 

 sold for use in concrete and grout. A small quantity of the spar 

 of the coarser size is sold for poultry grit. Crushed pegmatite for 

 these purposes brings a low price, usually around $3 a ton. 



The quarries and mills making roofing spar are situated in the 

 Adirondack region, and include those of the Crown Point Spar Co. 

 at Crown Point and the Barrett Manufacturing Co. at Ticonderoga. 

 The methods of milling are simple, being based on a system of 

 gradual reduction and sizing by screens. For the first step, a coarse 

 crusher of the Blake type may be used, followed by rolls. At the 

 mill of the Crown Point Spar Co., a higher grade of spar that is 

 sold to enamel ware manufacturers is made by crushing to fine 

 size in a chaser. The spar is first sent to the Blake machine, is 

 then dried and instead of passing through the rolls, goes to the 

 chaser. 



Manufacturers of enamel ware, glazed brick and terra cotta 

 consume considerable quantities of feldspar. The requirements 

 for these purposes are more exacting than for ordinary roofing spar 

 in that the material must be fairly free of iron or iron-bearing 

 minerals and have a relatively low point of fusibility. The feldspar 

 should also be fairly free of admixture with quartz, as the presence 

 of the latter tends to raise the melting point. As soda feldspar or 

 albite fuses at a slightly lower temperature than the potash varieties 

 orthoclase and microcline, it has preference among the glazed brick 

 and terra cotta manufacturers. The spar is prepared by fine grind- 

 ing by a chaser or a pebble or ball mill, the operations in a pebble 

 mill lasting about 5 hours and reducing the product to a size that 

 over 90 per cent will pass a 100-mesh screen. The glaze is added 

 to terra cotta by dipping or spraying with the prepared slip and 

 then burning in a kiln. 



Another use for the local product is in the manufacture of 

 opalescent glass. This requires a spar of about the same quality as 

 that for enamel ware, but may contain more quartz. The material 

 is also ground to about the same size. 



