- GeoRef, Copyright 2008, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Ultrasonic power is very effective in the mechanical analysis of fine-grained sedimentary rocks, such as clays, shales, and siltstones. An ultrasonic instrument which generates power from the tip of a cone-shaped mechanical transformer is much more effective than "tank-type" instruments. The ultrasonic method is very rapid and satisfactory for most fine-grained sedimentary rocks; however hard black shales are very refractory and require considerable time for complete disaggregation. Material coarser than clay-size is very satisfactorily disaggregated for size analysis; due to the micalike structure of some of the clay minerals, considerable alteration of grains probably occurs within the clay-size range, but this has no effect on size analysis for total sand, silt, and clay.