Salt water centric diatom frustule (skeleton). Diatoms are microscopic, unicellular algae that produce intricate silica (glass) cell walls that overlap like the top and bottom of a box. When diatoms die, their soft, internal parts deteriorate, leaving their hard, porous, glass skeletons behind. Diatoms are found in aquatic environments, and saltwater diatom skeletons appear in the fossil record as early as the Jurassic period (180 million years ago). In the United States, numerous deposits of...
