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Limescale deposits, from the surface of a water heater. Limescale forms on the surfaces of heating elements, kettles, boilers, etc. These deposits are composed of insoluble calcium carbonate, which is deposited from soluble calcium bicarbonate dissolved in water that has 'permanent hardness'. Calcium carbonate crystals possess many different shapes (polymorphs), depending on local crystalisation conditions when the deposits are formed. The cubic crystals are termed 'calcite' and the smaller, spherical crystals are termed 'vaterite'. The spherical forms are made up of many hexagonal vaterite plates and several can be seen in this image. Aragonite, a columnar polymorph is also present in this image. False-coloured SEM image. Image width is 570 microns.
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