Diatomite

Diatomite:
A light colored, fine-grained siliceous sedimentary rock that forms from a sediment rich in diatom remains.
Diatom Ooze:
A seafloor sediment that consists of at least 30% diatom remains.
Differentiated Planet: ...

diatomite -- Diatomite, or diatomaceous earth, is a siliceous sedimaentary rock formed from the accumulations of diatoms or other nanoplankton.

See also: Deposition, Delta, Strike, Soil, Tectonic