What is the nature of cell walls in diatoms? 

Explanation

The cell walls of diatoms are made of silica.
Their cell wall construction is known as frustule.
It consists of two thin overlapping shells that fit into each other such as a soap box.
When the diatoms die, the silica in their cell wall gets deposited in the form of diatomaceous earth.
This diatomaceous earth is very soft and quite inert.
It is used in filtration of oils, sugars and for other industrial purposes.