Often called DE or diatomite, this naturally occurring sedimentary rock is composed largely of the fossilized remains of diatoms (a type of hard shelled protist or chrysophyte). Diatomaceous earth is used for numerous agricultural, industrial, and commercial purposes, including metal polishes, liquid filtration, mechanical insecticide, digestive aids, toothpaste, plastic and rubber reinforcing filters, liquid absorbent, cat litter, chemical catalyst support, thermal insulation, a matting agent for coatings, and even as a stabilizing component of dynamite. This substance is mined in sites all over the world, but the oldest deposits are found in Germany, Colorado in the United States, the southern California Coast, and various regions of Canada, Denmark and the Czech Republic. Most diatomaceous earth consists of varying levels of diatoms, clay, and silica. Older deposits generally produce diatomaceous earth of higher purity, while those containing higher ratios of silica and clay are considered of lower purity and therefore less desirable.