Diatoms are also called as 'pearls of ocean', why? What is diatomaceous earth?

Diatoms have cell walls with unique characterstics. This is why, it is called as ‘pearls of ocean’. The unique characteristics of cell wall are as follows :
• It consists of cellulose impregnated with silica.
• It shows sculpturing and ornamentation.
Diatomaceous earth : Because of the presence of silica, cell wall of diatoms are indestructible. They pile up at the bottom of water body and leads to formation of ‘diatomaceous earth’ over billions of years. Diatomaceous earth is used in polishing, filtration of oils and syrups.