Hexagonal crystal system

The hexagonal crystal system is a classification of crystal lattices with a sixfold rotational symmetry axis and characteristic lattice geometry. Its conventional unit cell has equal basal edges meeting at 120° and a distinct perpendicular axis.

Crystal system: A classification of crystal lattices based on their symmetry and unit-cell geometry. The hexagonal system is one of the seven recognized crystal systems.
Sixfold rotational symmetry: Rotational symmetry in which a 60-degree rotation leaves an object unchanged. This defining axis gives the system its name and its characteristic symmetry.
Wurtzite: A crystal structure adopted by compounds such as zinc oxide, with tetrahedrally coordinated atoms and hexagonal symmetry. It is a common hexagonal structure type, distinct from the cubic zinc blende structure.
Trigonal crystal system: A crystal system whose point groups have a threefold principal rotational axis. Trigonal and hexagonal crystals can share hexagonal axes, but belong to distinct crystal systems.
Crystal lattice: An idealized, periodic arrangement of points representing equivalent positions in a crystal. Its translational symmetry underlies the hexagonal system’s unit-cell geometry.
Hexagonal Bravais lattice: The three-dimensional Bravais lattice with a hexagonal conventional cell and primitive lattice points. It is the Bravais lattice associated with the hexagonal crystal system.
Graphite: A carbon allotrope composed of stacked sheets of hexagonally bonded carbon atoms. Its crystal structure has hexagonal symmetry and strongly anisotropic bonding.
Cubic crystal system: A crystal system characterized by cubic lattice geometry and high rotational symmetry. Its equal axes and right angles contrast with the hexagonal cell’s distinct axial length and basal angles.
Unit cell: The smallest repeating region whose translations reproduce a crystal lattice. The conventional hexagonal cell expresses the system’s characteristic dimensions and angles.
Lattice parameters: The edge lengths and interaxial angles that specify a unit cell’s geometry. The conventional cell has equal basal edges, a distinct axial length, and a 120-degree basal angle.

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