Diatomsare also called as ‘pearls of ocean’, why? What is diatomaceous earth?

 Diatoms and desmids are inducted under chrysophytes, kingdom-Protista. These are the main producers in the ocean. They prepare food not only for themselves but also for the other life forms in the ocean. This is the reason they are also called as ‘pearls of ocean. Body of diatoms is covered by siliceous shell known as frustule.
‘Diatomaceous earth’ is the accumulation of large deposits of diatoms that forms a
siliceous covering extending for several 100 m_ formed in billions of years. The material obtained from these deposits is used in polishing and filteration of oils and syrups.