The cell walls construction of diatoms is known as Frustule which consists of two thin overlapping shells fitting into each other just as a soap-box. Their walls are made up of silica. When the diatoms die, the silica in their cell walls 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.

IN BRIEF:---

It consists of two overlapping shells...

It's walls are made up of silica...

When they die, silica gets deposited over it...

. The overlapping shells are fitted as soap box...