Diatoms are microscopic algae that live in both fresh and saltwater environments. They become impregnated with silicon from their environment as they grow, leaving a “skeleton” consisting of silicon dioxide (SiO₂) when they die. These diatoms are small. Many elongate forms are only 10–15 microns in length and 5 microns in diameter; others are spherical. They usually are free-floating, and a major component of oceanic plankton. They can be extremely numerous, and comprise the most important primary producers for small animal life in oceans. It is estimated that 25% of all organic carbon fixation (conversion of carbon dioxide and water into sugars by photosynthesis) on earth occurs in oceans due to diatoms. They also are a major source of oxygen. Most are not consumed, of course, and when the algae perish, their bodies accumulate, leaving silica deposits of up to 300 m thick in some areas. These compressed silicaceous deposits, consisting of 85–95% silicon dioxide, are mined for various...