Abstract

A systematic relationship exists between the texture of a rock type and the shapes of fragments produced by fracturing it. In visually isotropic rocks, the percentage of Zingg blades and spheres produced is directly dependent upon the texture, with aphanitic and glassy rocks producing the most blades and coarse-textured rocks producing the most spheres. The proportions of rods and discs are less predictable, perhaps because their basic specification are the same, as suggested by Smalley's random fracture theory. Weak anisotropy, still visible in hand specimen, has little effect on the shape of crushed fragments. This study shows the proportions of clast shape that should be produced by the initial breakup of various types of bedrock. Marked deviations from the observed trends may be characteristic of the environment in which the pebbles were later fractured and abraided.

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