Grain Size Analysis
GSI Protocol #02
Published: February 17, 2023
Prepared by: Stephen G. Hesterberg, Ph.D., Executive Director; Sarah W. Hutchins, M.S., Staff Scientist
MATERIALS
Glass jars with lids (200 mL)
5% sodium hexametaphosphate
Microbalance
Weigh boats
Label tape or chemical labels
Permanent marker
Plastic beakers, 250 mL (×1) and 1 L (×2) per sample
Drying oven
8-inch brass or stainless-steel nested mesh sieves from 4 to -4 phi at 1 phi intervals
INSTRUCTIONS
Disperse a standardized amount of sediment into a glass container using a solution of 100 mL of 5% sodium hexametaphosphate and 200 mL water for at least 72 hours. Between 10-100 g of sediment is recommended.
Wet sieve samples through a 63 μm mesh screen to separate course and mud fractions. Place into pre-weighed and labeled, plastic beakers (250 mL and 1 L, respectively).
Dry beakers containing the mud (<63 μm) fraction at 80°C for at least 72 hours, or until no moisture is detectable and re-weigh. Subtract the beaker weight and dry dispersant reagent weight to calculate mud fraction weights.
Dry coarse fractions at 90°C for at least 24 hours, or until dry, and re-weigh.
Process coarse fractions (>63 μm) through nested sieves ranging from -4 to 4 phi at 1 phi intervals. Shake nested sieves manually for ~2.5 min and then weigh each sorted dry sample.
Weigh sediment remaining in catch pan (<63 μm) and add to mud fraction weight to quantify the total silt/clay fraction.
Characterize mean particle size, sorting, and percent-gravel (>2 mm), -sand (2 mm – 63μm), and -mud (<63 μm) values using the following template spreadsheet. Characterization follows Wentworth (1922) and Folk (1974).
REFERENCES
Folk, R.L. (1974) Petrology of Sedimentary Rocks. Hemphills, Austin.
Wentworth, Chester K. (1922) A Scale of Grade and Class Terms for Clastic Sediments. Geology 30:377-392.
