Diatoms are a group of eukaryotic algae, and are a very common type of phytoplankton, or plankton that produces its own food. Most are unicellular, thought they are known to form basic colonies. They are most well known for their silica cell walls (or frustules), many of which are very beautiful, and cause diatoms to look like small jewels. Most species are microscopic, but they can reach up to two millimeters in length.
They are very widespread, and live in the open ocean, fresh waters, soil, and even on damp surfaces. They are vital to the planet’s ecosystem, and carry out up to 25% of Earth's carbon fixation.
When diatoms die, their shells do not decompose, and diatom deposits (which form in the ocean floor, lake beds, and rocks) have a variety of modern applications, such as paints, filtering agents, and abrasives.
I think they're lovely. =)