unit cell
Quick Summary
In crystallography, a unit cell is the smallest repeating unit that, when stacked together, forms the entire crystal lattice. It's the simplest geometric shape that embodies the crystal's structural characteristics. Think of it as a building block; repeating this block in all directions fills the entire crystal structure.12
The shape of the unit cell determines the crystal system it belongs to, and there are only a few basic shapes, meaning many different crystals can share the same unit cell type. An important feature of a unit cell is the number of atoms it contains, which helps determine the total number of atoms in the crystal. The dimensions and angles of the unit cell are known as its lattice constants. There are 14 fundamental types of unit cells, known as Bravais lattices, that can describe all possible crystal structures.2345
Ask Britannica AI about this topic
Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.
- Bravais lattice
…number of identical blocks, or unit cells, characteristic of the Bravais lattices. The French scientist Auguste Bravais demonstrated in 1850 that only these 14 types of unit cells are compatible with the orderly arrangements of atoms found in crystals.
Read More…number of identical blocks, or unit cells, characteristic of the Bravais lattices. The French scientist Auguste Bravais demonstrated in 1850 that only these 14 types of unit cells are compatible with the orderly arrangements of atoms found in crystals.
Read More 
calciteCrystal structure…1, are the true rhombohedral unit cell, which is the acute rhombohedron, and the cleavage rhombohedron setup. The true unit cell includes 2 CaCO3 with calcium ions at the corners of the rhombohedrons and CO3 groups, each of which consists of a carbon ion at the centre of a planar…
Read More…1, are the true rhombohedral unit cell, which is the acute rhombohedron, and the cleavage rhombohedron setup. The true unit cell includes 2 CaCO3 with calcium ions at the corners of the rhombohedrons and CO3 groups, each of which consists of a carbon ion at the centre of a planar…
Read More
ceramic composition and propertiesCrystal structure…overall box that describes the unit cell of that structure. By repeatedly translating the unit cell one box in any direction and by repeatedly depositing the pattern of ions within that cell at each new position, any size crystal can be built up. In the first structure (Figure 2A) the…
Read More…overall box that describes the unit cell of that structure. By repeatedly translating the unit cell one box in any direction and by repeatedly depositing the pattern of ions within that cell at each new position, any size crystal can be built up. In the first structure (Figure 2A) the…
Read More
hexagonal system…orderly stacking of blocks, or unit cells. The hexagonal unit cell is distinguished by the presence of a single line, called an axis of 6-fold symmetry, about which the cell can be rotated by either 60° or 120° without changing its appearance.
Read More…orderly stacking of blocks, or unit cells. The hexagonal unit cell is distinguished by the presence of a single line, called an axis of 6-fold symmetry, about which the cell can be rotated by either 60° or 120° without changing its appearance.
Read More- tetragonal system
…orderly stacking of blocks, or unit cells. The tetragonal unit cell is distinguished by an axis of fourfold symmetry, about which a rotation of the cell through an angle of 90° brings the atoms into coincidence with their initial positions. The elements boron and tin can crystallize in tetragonal form,…
Read More…orderly stacking of blocks, or unit cells. The tetragonal unit cell is distinguished by an axis of fourfold symmetry, about which a rotation of the cell through an angle of 90° brings the atoms into coincidence with their initial positions. The elements boron and tin can crystallize in tetragonal form,…
Read More - triclinic system
…orderly stacking of blocks, or unit cells. The triclinic unit cell has the least-symmetrical shape of all unit cells. Turquoise and other minerals such as microcline crystallize in the triclinic system.
Read More…orderly stacking of blocks, or unit cells. The triclinic unit cell has the least-symmetrical shape of all unit cells. Turquoise and other minerals such as microcline crystallize in the triclinic system.
Read More 
trigonal systemThe trigonal unit cell is distinguished by the presence of a single line called an axis of three-fold symmetry about which the cell can be rotated by 120° to produce a face indistinguishable from the face presented in the starting position. Selenium and other elements may crystallize…
Read MoreThe trigonal unit cell is distinguished by the presence of a single line called an axis of three-fold symmetry about which the cell can be rotated by 120° to produce a face indistinguishable from the face presented in the starting position. Selenium and other elements may crystallize…
Read More
crystalThe unit cellA basic concept in crystal structures is the unit cell. It is the smallest unit of volume that permits identical cells to be stacked together to fill all space. By repeating the pattern of the unit cell over and over in all directions,…
Read MoreA basic concept in crystal structures is the unit cell. It is the smallest unit of volume that permits identical cells to be stacked together to fill all space. By repeating the pattern of the unit cell over and over in all directions,…
Read More
principles of physical scienceSymmetryThe unit cell is the smallest block out of which the pattern can be formed by stacking replicas. The checkerboard in Figure 12 illustrates the idea; here the unit cell has been chosen out of many possibilities to contain one white square and one black, dissected…
Read MoreThe unit cell is the smallest block out of which the pattern can be formed by stacking replicas. The checkerboard in Figure 12 illustrates the idea; here the unit cell has been chosen out of many possibilities to contain one white square and one black, dissected…
Read More