A crystal lattice is a three-dimensional form that determines the shape of individual units of crystal. The lattice is not a physical thing; rather, it is the term that describes a physical shape. These lattices are larger than a crystal’s pattern, which determines the arrangement of individual atoms, and smaller than the crystal’s space group, which is made up of a collection of lattices. In many ways, the crystal lattice is the truest form of the crystal. If it is any smaller, it is incomplete and any larger and it is simply a multiple of crystals connected to one another.
A crystal is made up of a series of repeating patterns. If allowed to grow without interruption, that pattern would continue on forever with no variation. Such situations are uncommon, though, as things such as heat, gravity and chemical impurities can have drastic effects on crystal growth. There are three terms that describe a crystal’s shape: pattern, lattice and grouping.
The pattern of a crystal describes the way the individual atoms or molecules are arranged within the structure. This is the smallest of the descriptions, but it has a major impact on the way the final crystal is put together. Generally speaking, this is the most stable way for the individual particles to connect, which makes most crystals atomically and chemically stable. No matter how large a pattern is, it will continuously repeat if given enough room.
The next step up in size is the crystal lattice. This form describes a series of points and lines in three dimensions that will be filled by the pattern. The shape of the lattice is determined by the pattern, as the molecular shape of the crystal will repeat into a distinct and stable shape. The crystal lattice makes a crystal take on a district and recognizable shape, such as table salt appearing like small cubes.
Since a crystal lattice is so stable and predictable, there are only a handful of different possible shapes. All the shapes are variations of cubes, boxes, rhomboids and hexagons although they go by many different names. Even though two lattices may appear to be identical cubes, the inner structure of points might be different, giving it a different name and, technically, a different shape.
The largest description of a crystal is the grouping. This form describes the pattern that individual lattices will take as they replicate. This final grouping has hugely variable size as it can describe any collection from two lattices on through infinity.