This rock is a mixture of dolomite and gypsum.

Cornieule - also called crystallized dolomite - is basically a dolomite full of cavities that contain gypsum. Due to dissolution of the gypsum, the remaining rock has a typically porous aspect, like a sponge, and is highly permeable.

It’s not good when workers constructing tunnels come across this rock as it’s usually saturated with water and when the machines bore into it, the water is released under high pressure into the tunnel.

We find yellow-coloured bands of rauhwacke in the National Park, at Margunet for instance.

Gypsum is ductile and therefore represents a mechanically weak stratum in the whole series of sedimentary rock. During the formation of the Alps, the greatest thrust movements occurred where there were strata of gypsum. Moreover, gypsum functioned as a lubricant, incorporating at the same time fragments of the partly destroyed dolomite.