Diatomaceous earth, also known as D.E., diatomite, or kieselgur/kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 3 micrometres to more than 1 millimeter, but typically 10 to 200 micrometres. Depending on the granularity, this powder can have an abrasive feel, similar to pumice powder, and is very light as a result of its high porosity. The typical chemical composition of oven-dried diatomaceous earth is 80 to 90% silica, with 2 to 4% alumina (attributed mostly to clay minerals) and 0.5 to 2% iron oxide.
Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae.