composed primarily of piece of rock diatomite diatomite particle Diatomite is easily crumbled into a fine white to off-white powder. The powder has a particle size ranging from less than 3 micrometres to more than 1 millimetre, but typically 10 to 200 micrometres. The diatoms in each deposit contain different amounts of silica, depending on the age of the deposit. The species of diatom may differ among deposits. The species of diatom is dependent upon the age and paleo-environment of the deposit. In turn, the shape of a diatom is determined by its species. 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. piece of diatomaceous earth particle of diatomaceous earth particle of diatomite A piece of rock which is primarily composed of diatomite: the fossilized, siliceous remains of diatoms mixed with varying amounts of other clays and minerals. kieselgur particle piece of diatomite D.E. kieselguhr particle diatomaceous earth