A soft, crumbly sedimentary material — also called diatomaceous earth — composed of fossilized diatom shells, used as a filtering agent and for various other industrial applications. Food plants use food-grade kieselguhr to clarify beer, wine, juices, and syrups, trapping haze particles in its porous structure. The grade must be food-safe, as industrial grades may carry unwanted contaminants — and spent filter cake requires proper disposal as it may contain concentrated impurities. Calcined grades filter more coarsely than natural ones. Proper dust control protects workers handling it.