Image Gallery: Crystal shapes
Minerals can be identified by the shape of their crystals or crystallography. The shapes of crystals are determined by a number of factors such as the size and length of their surfaces (known as 'faces') and edges, as well as the angles between these. These shapes are named after their geometry - for example, crystals based on cubes belong to the 'cubic or isometric' crystal group. There are seven main crystal groups or systems, as shown here.