GRAIN-SIZE ANALYSIS BY LASER DIFFRACTOMETRY - COMPARISON WITH THE SIEVE-PIPETTE METHOD

Results of a traditional sedimentation technique for grain-size analys is (the sieve-pipette method) were compared with those of a laser diff raction grain-size analyser, the Coulter LS-100, Milled quartz samples and silty soil samples were used to investigate the effect of particl e shape. The reproducibility of the Coulter LS-100 was better than tha t of the sieve-pipette method, except for the sand fraction. The agree ment between the two methods is strongest for the milled quartz sample s. The Coulter LS 100 underestimated the clay content of the silty soi l samples and generally overestimated the clay content of the milled q uartz samples. This indicates the importance of particle morphology. T he milled quartz grains are very angular and somewhat elongated wherea s the clay minerals in the clay fraction of the silty soil samples usu ally have a platy shape. Reduced major axis relationships are calculat ed which may be used to convert Coulter LS-100 results to those of the sieve-pipette method. Correlation is strongest for percentiles size d ata. The Coulter LS-100 underestimates the clay, but correctly estimat es the and fraction. This results in a weak relationship for the total silt fraction as measured by the two techniques. Therefore, an altern ative method is proposed for estimating this fraction. A comparison of our data with published data and relationships suggests that the cali bration relationships are quite robust as long as the clay mineralogy of the samples is similar. (C) 1998 Elsevier Science B.V. All rights r eserved.