Crystal growth is the process where a pre-existing crystal becomes larger as more growth units (e.g. molecules, ions) add in their position in the crystal lattice is developed into a crystal and further growth is processed. A crystal is defined as being atoms, molecules, or ions arranged in an orderly repeating pattern, a crystal lattice, extending in all three spatial dimensions. So precious stone development varies from development of a fluid bead in that during development the atoms or particles must fall into the right cross section positions all together for a very much arranged gem to develop. The schematic shows a very simple example of a crystal with a simple cubic lattice growing by the addition of one additional molecule. When the molecules or ions fall into the positions different from those in a perfect crystal lattice, crystal defects are formed. Typically, the molecules or ions in a crystal lattice are trapped in the sense that they cannot move from their positions, and so crystal growth is often irreversible, as once the molecules or ions have fallen into place in the growing lattice, they are fixed in place.