Experiment 8: Particle Size Distribution

INTRODUCTION

One of the methods used for determining grain size distribution is sieve analysis. After the grain size distribution has been determined, the depositional history of the rock may be inferred from graphical analysis of the grain size distribution. The distribution of sizes of the grains in sediments is related to: (1) the availability of different sizes of particles in the parent matter from which the grains are derived, and (2) the processes operating where the sediments were deposited, particularly the competency of fluid flow (in other words, the history of sedimentary processes).

Measurement of the grain size distribution will yield a plot of the cumulative mass percent (frequency) of ranges of grain sizes versus the PHI-scale used for particles size notation, the surface area of the rock per unit of pore volume and of bulk volume, and the surface area per unit of grain volume of the sediment.

EQUIPMENT AND PROCEDURES

In general, the procedure is to carefully crush the rock with an impact crusher (not a grinder) to obtain individual grains. A set of sieve trays is assembled with the finest screens at the bottom (Figure A8.1). In sieve analysis, it is assumed that the grains caught on the individual screens have sizes that are smaller than the openings of the screen above and larger than the screen that they are resting on. The amount of sand caught on each screen in the stack is weighed and, as a first approximation, the average grain diameter is assumed to...