Figure 4

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Dusts photographed under a scanning electron microscope. (A) Silicon dioxide dust. Aggregate of nanoparticles (grains smaller than 100 nm) of “amorphous silica”. (B) Sommières earth. Assemblage of fibrous sepiolite crystals. (C) Diatomaceous earth from a pest management company (DE-pro). Frustules (small shells) of “unprocessed” diatoms (unicellular microscopic algae) made of “amorphous silica”. (D) Diatomaceous earth from the supermarket (DE-hom): diatom frustules probably transformed by intense heating, transforming the “initially amorphous silica” into “a cristobalite-type crystalline structure”, suitable for use as a swimming-pool water filter.
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