The ash content of Equisetaceae and Gramineae/Poaceae may
consist of up to 50-70% silica.11 Some polyamines, carbohydrates,
proteins, and glycoproteins from diatoms and sponges
have been reported to be capable of polymerizing silicic acid
at neutral to acidic pHs.12 Some plant carbohydrates and proteins
have also been shown to play a key role in biosilica polymerization.
13 In the biosphere, silica is accumulated predominantly
in the form of amorphous silica (opal or silica gel)