Diatoms are single-celled brown algae whose cell membranes have the property of binding the silica present in water. Diatoms form a kind of "armour", also called "frustules", consisting of hydrated amorphous silica, similar to opal.



This silica armour occurs in various types, shapes and sizes that can vary between 5 and 40 microns. More than 10,000 species or shapes of diatoms are known.

After the organism has died, the silica armour is left behind unchanged. On particular sea beds or in certain lakes where the water contains silica, reproduction can be so extensive that considerable deposits are formed, and after fossilization these yield a lightweight, very porous ore: diatomite, the raw material for Clarcel.