Crystal Structure

Polyhedral crystal symmetry summary

• Isometric or cubic (15 forms) or Non-isometric or non-cubic (32 forms)
  
• Six Lattice Systems: cubic, hexagonal, tetragonal, orthorhombic, monoclinic and triclinic (from most to least symmetrical)
• 14 Bravais Lattices result from combining the six crystal systems with all possible translations around a center gives
• 32 Point Groups or Classes result from other symmetry operations that do not change the crystal's appearance, such as rotation around at least one point

Special crystal effects may be related to asymmetry

Crystals belonging to classes without centers of symmetry, such as cane sugar, quartz, or topaz, often generate electricity when struck or stressed, a quality known as piezoelectricity.

Impurities and radiation alter the properties of most naturally formed crystals

Other minerals and chemicals mixing in as minerals solidify in nature, and even exposure to (usually naturally occurring) radiation, can produce diverse colors in crystals with the same chemical composition.

Iron oxide gives the quartz crystal carnelian its distinctive orange hue. Amethyst is naturally irradiated quartz with iron impurities; radiation causes iron ions to line up within the crystal's lattice in a certain way, producing the stone's violet color.

What about crystal systems?