Diatoms are also called as 'pearl of ocean', why? plz tell me its urgent!!!!!!

The diatoms- the unique organisms - are sometimes called the jewels of the sea because of their distinctive cell walls. The cell wall of diatoms is chiefly composed of cellulose impregnated with glass like silica. It shows sculpturing and ornamentations. That is why, diatoms are also called as 'pearl of ocean '.