At low magnifications, the St. Peter Sandstone from working quarries in northeastern Illinois was found to be subangular to rounded, frosted in appearance, and occasionally covered with localized, relatively large, terminated quartz overgrowths. At higher magnifications, however, the frosted surface of the quartz grains was found to consist of a layer of micron-sized, coprecipitated quartz crystals and kaolinite flakes. The delicate nature of the crystals suggests that these surface features are secondary, having a postdiagenetic origin. Based on the scanning electron microscope data presented, it is impossible to tell the state or nature of the original sand surface before deposition.

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