What is the nature of cell wall in diatoms?

(a) In diatoms, the cell walls form two thin overlapping shells which fit together as in a soap box.
(b) Their walls are embedded with silica making it indestructible.
© They pile up at the bottom of water reservoirs and form big heaps called diatomite.
(d) Diatomite is used in filtration of sugars, alcohol and antibiotics.