Electron microscopy of chemical solution and mechanical abrasion features on quartz sand grains

Abstract

Crystallographically oriented etch pits have been observed on quartz sand grains from marine environments, using an electron microscope. Similar features have been produced by etching quartz in the laboratory with hydrofluoric acid and sodium hydroxide. Examination of quartz sand grain surfaces from beaches of different wave intensities along the Atlantic and Gulf coasts of the United States suggests a relationship between the effects of such chemical solution features and mechanical abrasion on sand grains. Sand grains from beaches with low wave activity exhibit oriented etch pits readily attributed to the solution of quartz by sea water. These features are the surface expression of defects within the crystal. Sand grains from beaches with moderate wave energy show a combination of chemical etch features and those phenomena thought by KRINSLEY and TAKAHASHI (1962a) to be caused by grain-to-grain impacts, while grains from high-energy beaches predominantly show impact features. If the correlation shown by the results are valid, the relative number of chemical and mechanical features on sand grains can be used to determine energy conditions along ancient shorelines.