Diatomite

Diatomite is a siliceous sedimentary rock composed mainly of the fossilised skeletal remains of diatoms, which are single-celled organisms related to algae. It has a porous structure, which makes it ideal for use as insulation or as a filtering material (its primary use). Most Victorian diatomite, however, is too impure for use as a filtering agent. When dry, diatomite has the appearance of chalk but is much lighter and is chemically inert.

Diatomite is a porous, low-density, sedimentary rock formed by the accumulation and compaction of diatoms which may comprise 90% or more of the dry weight of the rock. The physical properties of diatomite have led to its use in many commercial applications, the most common being for the filtration of liquids or as a filler, for example, in paints. Other uses of diatomite include insulation (fire bricks), fine abrasion (in some toothpaste and polishes) and as a pesticide.