Diatom is generally seen to be found in both freshwater and marine water.
Diatoms have silica in the shell walls which are transparent and overlapping in nature.
Their cell wall is known as a shell or frustule which is composed of cellulose.
The form of food in diatoms are leucosin (chrysolaminarin) and fats (oils).
Their cell walls do not get destroyed after death so, at the bottom of the sea, very big rocks of dead diatoms are formed which are called as diatomite or diatomaceous earth or kieselguhr.