Abstract

Sphericity of quartz grains in sediments determined by three dimensional measurement varies from 0.5 to 1.0 around a mean of 0.75 sphericity units and is approximately normally distributed. Differences in sphericity of quartz grains between arkoses, graywackes, and quartzites are not large and arkoses are least spherical, graywackes intermediate, quartzites most spherical; the differences are not statistically significant on the basis of these 2700 measured grains.

The roundness determined by visual comparison of quartz grains from 125 micron size-grade shows a similar trend from least round in arkoses to most round in quartzites, but the frequency distribution of roundness is markedly nonnormal and the conclusions based on statistical analysis are approximate.

The magnitude of variation in sphericity and roundness in arkoses is greatest among grains and least among samples, in low rank gray wackes it is moderate in both, whereas in quartzites it is least among grains and greatest among samples; this difference requires a sampling plan specifically designed for each rock type if the analysis of shape of quartz grains is to lead to significant differences at the formation level.

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