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Diatomaceous earth. (A) Scanning electron micrograph showing the calcified diatoms, ×15 000. (B) Electron microprobe analysis shows only silicon (Si); the oxygen with which silicon is combined in silica (silicon dioxide, SiO2) is of too low an atomic number to register. The titanium (Ti) peak derives from the sample holder.
(Courtesy of Dr D Dinsdale, Leicester, UK and Professor B Nemery, Leuven, Belgium.)
