Diatom frustule, SEM

False-coloured scanning electron micrograph of a fragment from a diatom frustule. Diatoms are types of algae which are often unicellular though can exist in colonies. They are found in most aquatic environments including fresh and marine waters. A frustule is a hard external shell made of silica which acts as a skeleton to support the diatom. Horizontal width of image is 34.5 micrometres.