Clay-sized quartz particles from the suspended load of the Mississippi River display subspherical and well-rounded morphologies. When viewed under a scanning electron microscope, the grain surfaces exhibit overlapping caps of precipitated SiO2 plates and occasional etch pits formed by chemical dissolution. Such morphologies indicate that the grains are multicyclic in origin and have been derived from weathering pedogenic environments. In comparison, primary clay-sized quartz grains from glacial drift and gneissic detritus are wedgelike and angular, and their surfaces are characterized by mechanically produced features such as breakage blocks and conchoidal fractures. Thus, grains from different sedimentary provenances display distinctive shape and surface texture features. Morphological analysis of clay-sized quartz particles should become an important diagnostic tool in understanding the complex history of terrigenous deposits, because the fine particles exhibit the same source-indicative features as the coarser silt- and sand-sized grains.

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