frustules

This usually leaves the frustules bright and sharp.

Scientific American Supplement, No. 1178, June 25, 1898 Various

-- Microscopic cellular bodies, growing in fresh, brackish, and sea water: free or attached, single, or embedded in gelatinous tubes, the individual cells (frustules) with yellowish or brown contents, and provided with a silicious coat composed of two usually symmetrical valves variously marked, with a connecting band or hoop at the suture.

Scientific American Supplement, No. 384, May 12, 1883 Various

Diatomaceae, living in a medium which may contain only one part in 10,000 by weight of dissolved silica, or even less than that amount, should be able to separate this substance to form their exquisitely ornamented frustules is one of the most striking facts in natural history, whether we regard it in its physiological or its chemical aspects.

Scientific American Supplement, No. 595, May 28, 1887 Various

As an illustration of their minute size it may be mentioned that a single drop of water from the saucer of a flower-pot at Hertford, mounted as a microscopic slide, was found to contain 200,000 separate frustules of

Hertfordshire Herbert Winckworth Tompkins 1901

Except for the precipitous slopes and regions swept bare by the submarine currents, the ocean floor is covered with primeval oozes which have been accumulating for eons deposits of varied origins; earth-born materials freighted seaward by rivers or worn from the shores of continents by the ceaseless grinding of waves; volcanic dust transported long distances by wind, floating lightly on the surface and eventually sinking into the depths to mingle with the products of no less mighty eruptions of submarine volcanoes; spherules of iron and nickel from interstellar space; and substances of organic origin – the siliceous skeletons of Radiolaria and the frustules of diatoms, the limey remains of algae and corals, and the shells of minute Foraminifera and delicate pelagic snails.

Undersea (historical) Rachel Louise Carson 2007