﻿Plate 22 





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Photomicrograph of bluestone, x 25 diameters. The clearer grains are 

 quartz and indicate the approximate size of other original constituents. 

 In this case the alteration of the feldspars and ferromagnesian originals 

 is so complete that their products form an indeterminable complex aggre- 

 gate of closely interlocked granules, flakes, and fibers of extremely fine 

 texture. 



Photomicrograph of first grade medium grain bluestone, x 25 diameters. 

 Taken to show angular and interlocking grains indicating secondary 

 growth and a complete lack of reeding structure. The clear grains are 

 quartz; the rest of the field is made up chiefly of secondary derivatives 

 from the original feldspars and ferromagnesian minerals. 



