Diatomaceous earth is the sediment formed from the deposition (over aeons) of the skellies of dead diatoms. Said skellies are essentially silica but the fine structure (often referred to as "decoration") varies according to the species of diatoms. Those of you who have "serious" microscopy in your background may have experienced the test slides made by mounting specimens of dead diatom skellies, from selected species, on a microscope slide. The species were chosen so that you could test the resolving power of microscope objectives; the higher the resolution of the lens, the finer were the decorations you could discern.

Enough thread drift.

Cheers, Rowan