Diatomaceous earth is formed of the remains of fossile diatoms.
It consists of the shells of radiolarians and diatoms of very varied forms,
whose structure is made up of 85-90% salicic acid (SiO2) and 4% Al2O3 and is electrically charged.
Depending on the age of the biological ocean developement, large deposits were formed, from which the diatomaceous earth is recovered by open cast mining. Depending on the origin (California, France or Germany), there are differences in the purity, colour, form and filter effect. There are round shapes, needle like shapes, shapes like little ships, square plates, or fan forms.
The shells in the shape of needles provide the best clearing action, but the filter becomes easily choked. Diatomaceous earth consisting mostly of round plates has a fast clearing action, but is not very effective. Therefore a mixture is usually used. A larger size of the pores in the filter increases the throughput at the cost of the clearing effect.