ANCIENT SANDS 



107 



Fig. 31. Microphotograph of grains of pyrite in quartz in ancient sands 

 of Witwatersrand, South Africa (x 70). The rounded grains show later 

 growths of pyrite, formed after the deposition of the sands, which 

 follow crystal planes, and tend to obliterate the roundness of the original 

 pyrite sand grains (from Ramdohr, 1958). 



