Soil gypsum determination

The methods for gypsum content determination in soils are summarized and their applicability discussed. Special attention is given to the critical step of sample preparation, stressing the elimination of the oven heating at temperatures surpassing 40°C. Wet methods are unsuitable for soils rich in gypsum or containing other sulfates. Instead, oven-based methods playing on the mass variations due to the release of constitutional water of gypsum are preferable. Under laboratory settings, we recommend two existing methods: one directly measuring the loss of mass on heating and the other exploiting the gypsum–bassanite phase change under controlled conditions. Both reflectance and X-ray fluorescence (XRF) provide nondestructive methods for quick gypsum appraisal, and combining both methods increases the accuracy. The results are easily calibrated with gravimetric methods.