Diatoms are a type of protist, a microscopic organism. What makes diatoms remarkable is they have shells made from organic compounds and silica. These shells are left behind when a diatom dies.Diatomaceous earth is a mineral that is formed from fossilized diatom shells, and this is mined for a number of industrial purposes.The product of diatoms, diatomaceous earth, is typically used, though living diatoms are also useful.iatoms are often used to filter water, particularly water in hot tubs and swimming pools. However, a vast variety of fluids can be filtered with diatoms, including different syrups, alcoholic beverages, medicines, solvents and other chemicals.