Why do mineral crystals have specific shapes?
The specimens on display in the Mineral Gallery of the New York State Museum exhibit many different shapes. There seems to be an endless number of crystal forms, which, at first glance, can be quite confusing. While it is true that there are many variations, all crystal shapes can be placed into a small number of crystal systems. The crystal systems are based upon similarities in the geometry of mineral crystals. Since the outward form of a crystal depends the internal arrangement of atomic building blocks, it is not surprising that within each crystal system there are basic building blocks that have characteristic proportions and angles. Nature likes to keep things simple. The simplest crystal shape, a cube, is Nature’s attempt to pack the greatest number of atoms into the least space. If all atoms were the same size, all crystals would belong to one crystal system. However, atoms vary a great deal in characteristics such as size and electrical charge. For this reason, all atoms canno
