False-coloured Scanning Electron Micrograph (SEM) of microscopic crystals of calcium carbonate. Calcium carbonate has many polymorphs (different shaped) crystal forms. The cubic crystals shown here are termed 'calcite' and the smaller, sperical crystals are termed 'vaterite'. The spherical forms are made up of many hexagonal vaterite plates and several can be seen in this image. No aragonite, a spiky or columnar polymorph is present in this image. Calcium carbonate occurs naturally in many rocks, such as limestone and other chalky rocks and is relatively inexpensive to extract. It has a multitude of different industrial uses and is the most common active ingredient in antacid tablets. Image width is 116 microns.