414 



GEOLOGY, 



line rocks composed of dominant quartz and feldspar of any kind, with 

 mica, hornblende, or other minerals in subordinate amount. In scientific 

 literature as it now stands, granite consists of quartz, feldspar, and 

 mica, the feldspar being of the alkali-potash or soda variety (ortho- 

 clase, microchne, or albite), and the mica, either muscovite or biotite. 

 In the type form the crystals are distinct and sometimes large (Fig. 344). 

 They are intimately mingled with one another, and in growing, interfered 

 more or less with each other and so became interlocked. The granites 



Fig. 345. — Graphic granitic (or pegmatitic) texture. Nearly natural size. 

 (Photo, by Church.) 



are among the most common and easily recognized of the holocrystal- 

 line rocks. Their color is mainly dependent upon the feldspar, the 

 red and pink varieties of the mineral giving rise to red granite, and the 

 white varieties to gray granite. 



