Axis of symmetry - An imaginary line drawn through the center of a crystal that replicates the exact shape if the crystal is turned to 360°. Minerals can have symmetry on their x axis (horizontal symmetry), on their y axis (vertical symmetry), and both their x and y axes. Symmetry can also be calculated on degrees, which depends on how often a crystal must be rotated to bring out symmetry (i.e. a hexagon has sixfold symmetry on a 60° angle). (See Crystals in mineral properties for more information.)