The two recumbent statues at the cathedral of Aosta (1371-1460) which date to the late Gothic period are characterized by material that is unusual both for this area and for this kind of monument: mostly gypsum alabaster, and anhydrite. The petrographical study of the texture showed that in both cases metamorphic rock was involved, and that the gypsum results from the transformation of the anhydrite as a result of retrocession and hydration. Specific mineralogical research was carried out (x-ray diffraction and infrared examination) and confirm that it is very likely that the material was found locally in quarries which remain to be uncovered.