Diatomaceous earth is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white powder, composed of the fossilized remains of diatoms, a type of hard-shelled algae. It is widely used for filtration, as an abrasive, and as a natural insecticide due to its ability to absorb lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate.