tetragonaali

Tetragonaali (tetragonal) is a term used in crystallography and mineralogy to describe crystals and minerals that belong to the tetragonal crystal system. In this system the unit cell has two equal axes a and b and a third axis c that is different in length, with all interaxial angles at 90 degrees. In practical terms this means a square base that is stretched or compressed along the c axis.

Lattice centering in the tetragonal system can be primitive (P) or body-centered (I). The system is one of the seven crystal systems and includes minerals such as zircon (ZrSiO4), rutile (TiO2), cassiterite (SnO2), scheelite (CaWO4) and chalcopyrite (CuFeS2). The tetragonal arrangement commonly results in anisotropic physical properties, with properties varying along the c axis relative to the a,b directions.

Symmetry elements of tetragonal crystals include a fourfold rotation axis, and higher-symmetry groups may have mirror planes and other rotational symmetries. This symmetry influences X-ray diffraction patterns and crystal growth habits.

The term derives from Greek tetra- “four” and gonia “angle.” In Finnish, tetragonaali is the standard adjective for this crystal system.