gypsum

Fracking, in this regard, is no different from gypsum mining, or some kinds of industrial agriculture.

The sand dunes were relentlessly mined in the past century; power lines and a gypsum plant split the park.

It is sometimes mixed with lime or gypsum, and dried with heat, and sometimes with animal charcoal or peat charcoal.

"There is an extensive underlying layer of gypsum, here," he said.

At the top there is a small aperture, which is hermetically closed with gypsum.

The difficulty of boiling them soft arises from an excess of gypsum imbibed during their growth.

The gypsum reposing on the mud is composed of plates in such close juxtaposition as to resemble an artificial pavement.