English: Diatomaceous earth, also known as diatomite or kieselgur, as viewed under bright field illumination on a light microscope. Diatomaceous earth is a soft, siliceous, sedementary rock made up of the cell walls/shells of single cell diatoms and readily crumbles to a fine powder. Diatom cell walls are bivalve, i.e. made up of two halves, and are made up of biogenic silica; silica synthesised in the diatom cell by the polymerisation of silicic acid. This sample consists of a mixture of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms. The primary uses of diatomaceous earth are for cleaning (scouring), filtration, heat-resistive insulation and as an inert absorbent substrate. One of the most famous uses was by Alfred Nobel who developed dynamite; a mixture of diatomaceous earth and nitroglycerin. This image of diatomaceous earth particles in water is at a scale of 6.236 pixels/μm, the entire image covers a region of approximately 1.13 by 0.69 mm.