Origin, shaping and significance of quartz sand grains

Abstract

Abstract Quantitative and qualitative studies of the shape characteristics of both natural and artificially prepared particles combine with evidence from diverse other sources to suggest strongly that the quartz of granitic rocks and gneisses is repeatedly fractured and healed in an intricate manner before being presented at the Earth's surface and that, in the zone of weathering, this quartz is parted along some of the resulting incipient fractures. The quartz fractures are thought to originate when granitic rocks pass through a state wherein their quartz is brittle while the surrounding feldspar is still ductile. Experimental evidence supports the view that the pattern of fractures affecting granitic quartz is characteristic of the breakage of particles of a brittle solid embedded in a ductile, deforming matrix. This process produces particles that are often remarkably equant and rounded for breakage products. Breakage along incipient fractures can account for the main changes in shape and size that affect quartz grains after emergence from primary source rocks. For most quartz sand grains, attrition needs to be cited only as a finishing process in bringing about their present shapes. Some geomorphological effects of quartz breakage are discussed.