All minerals are crystalline, with orderly and repeating arrangements of atoms. Growth occurs by the addition of atoms to the arrangement. If growth takes place in an open space or in soft material, a crystal, reflecting the internal atomic arrangement may form. Although ideal crystals are perfect shapes, many actual crystals are distorted due to variations in growth over time. Although there are enormous variations in crystal shapes, they can all be grouped into six crystal systems based on the geometry of the internal structure.