Crystal
![A crystal of amethyst quartz](/Images/godic/202502/21/Amethystemadagascar20446.jpg")
![Halite (table salt, NaCl): Microscopic and macroscopicMicroscopic structure of a halite crystal. (Purple is sodium ion, green is chlorine ion.) There is cubic symmetry in the atoms' arrangement.Macroscopic (~16cm) halite crystal. The right-angles between crystal faces are due to the cubic symmetry of the atoms' arrangement.](/Images/godic/202502/21/Sodium-chloride-3D-ionic0446.png")
![Halite crystal (Macroscopic )](/Images/godic/202502/21/Selpologne0446.jpg")
![As a halite crystal is growing, new atoms can very easily attach to the parts of the surface with rough atomic-scale structure and many dangling bonds. Therefore, these parts of the crystal grow out very quickly (yellow arrows). Eventually, the whole surface consists of smooth, stable faces, where new atoms cannot as easily attach themselves.](/Images/godic/202502/21/Crystal_facet_formation.svg0446.png")
A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations.