Abstract
Summary: The technique for preparing sand grain surfaces for electron microscope study is described. Three stages in the development of secondary silica overgrowths are recognized: first, formation of rhombohedral projections; second, overlapping of rhombohedra to give planar faces; and third, formation of euhedral crystals. Electron micrographs of Penrith Sandstone grain surfaces lacking overgrowths show the presence of irregularly shaped abrasion blocks and conchoidal fractures comparable with those described from modern aeolian sands. The source of the secondary silica is attributed to the solution of the silica dust produced during grain fracture and surface abrasion.

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