Diatoms hidden inside a grain of sand, SEM

False-coloured scanning electron micrograph of three diatoms hidden inside a cavity of a grain of quartz sand. The sand was collected from a beach on the Florida gulf coast in the USA. Some of the sand at Florida's white gulf coast beaches is more than 99% quartz. Quartz or silica is a primary component of typical beach sand which forms when rock is weathered away (gradual wearing down of rock by e.g. temperature, wind, waves, rain, freezing and thawing, and the burrowing of plants and animals into cracks). 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. Horizontal width of image is 100 micrometres.