58 



NEW YORK STATE MUSEUM 



Production of stone in 1915 



GRANITE 



Granite is both a specific and a general term. When used in the 

 restricted scientific sense it means an igneous rock of thoroughly 

 crystalline character in which the chief constituents are feldspar, 

 quartz and mica. Such a rock has a massive appearance ; that is, 

 the constituents are uniformly distributed in every direction, and 

 owing to the predominance of the feldspar and quartz the color is 

 rather light, commonly gray or pink. As a variation to the uniform 

 distribution of the minerals, the latter may develop a plane parallel 

 arrangement through the influence of compression when the mass 

 was still deeply buried in the earth's crust. A granite with this 

 parallel or foliated texture is known as a granite gneiss. 



The commercial definition of granite is much broader than that 

 given and includes almost • any of the crystalline silicate rocks 

 (usually igneous) that possess the requisite physical qualities for 

 use as architectural or monumental stone. In most cases the com- 

 mercial product is actually a granite in the true sense, but not in- 

 frequently it may be a syenite which lacks quartz, or a diorite con- 

 sisting of plagioclase, feldspar and hornblende, or anorthosite which 

 contains little else than basic plagioclase feldspar. So-called black 

 granites are mainly gabbros and diabases with a large proportion of 

 the iron compounds — pyroxene, hornblende and magnetite. 



The broader usage will be followed in the present classification, 

 as all the above-named rocks are quarried in this State. The only 

 silicate rock not included under granite is diabase or trap which, on 

 account of the special features surrounding its production and 

 uses^ is classified by itself. 



