Plural of frustule; the siliceous cell walls of diatoms (tiny single-celled algae), consisting of two interlocking halves.
From Latin 'frustulum' (a small piece), diminutive of 'frustum.' In the 1800s, this term was adopted by botanists to describe the transparent casings of diatoms.
Diatom frustules are literally made of glass-like silica and have intricate geometric patterns—under a microscope they look like the most beautiful architecture in nature!
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