Coral sand sample, coloured scanning electron micrograph (SEM). These small pieces of broken coral were obtained from a sand sample taken at a depth of 15 metres in the Red Sea. The sand mainly consists of calcium and silicate mineral products of animal origin. Shells include those of tubular worms, as well as coral debris and marine snail shells, as well as parts of sponges. Magnification: x53 when printed at 10 centimetres across.