Abstract

The reliability of visual estimates of relative proportions of minerals in a particle aggregate was found to be not significantly affected by differences in particle composition, by color or composition of background material, by relative differences in academic training of geologists, or by use or non-use of a visual comparison chart. A point count of 16 points gives a level of precision equal to that of the visual estimates. A point count of 64 points gives a level of precision that is twice as high as that of the visual estimates. A 95 percent level of significance is applied to the results of the graeco-latin square and analysis of variance tests of the 384 different visual estimates used in the study.

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