# Sedimentology (Particle size distribution parameters)

The Inclusive graphic standard deviation (sorting) value of this claystone sample is negative (-1.29). Is this right to be considered as very well sorting ? However, the bivariate plots of depositional environment do not include negative values on the axis of the standard deviation.

Note: The granulometric data was obtained by laser diffraction technique. The formula of the inclusive graphic standard deviation after Folk 1974: $\sigma_1 = \frac{\phi_{84} - \phi_{16}}{4} + \frac{\phi_{95} - \phi_{5}}{6.6}$