Calcium phosphate crystal, coloured scanning electron micrograph (SEM). Crystalline materials have their atoms placed in regular lattices that can form geometric shapes like this. Calcium phosphate crystals contain both calcium (Ca) and phosphate (PO4) ions, but the precise ratio varies according to the crystal structure. Calcium phosphates are used in dental materials and also in foodstuffs. Magnification: x400 when printed 10 centimetres wide.
