triklinische

Triklinische, or the triclinic crystal system, is one of the seven crystal systems used in crystallography. It is defined by three unequal lattice parameters a, b, and c and by angles α, β, and γ that are all oblique and not equal to 90 degrees. The unit cell is the most general parallelepiped, and no axis symmetry is imposed by the lattice, giving the triclinic system the lowest symmetry among crystal systems.

In terms of symmetry, triclinic crystals possess only two possible crystallographic point groups: 1 (no symmetry) and Ci (inversion center). Accordingly, the conventional space groups are P1 and P-1, and the Bravais lattice is primitive (P).

Physically, triclinic crystals are typically anisotropic, with three distinct principal refractive indices, and they are biaxial in optical character. Their low symmetry leads to complex crystal habits and often subtle twinning patterns. Because of the lack of symmetry constraints, triclinic minerals and crystals can exhibit a wide range of shapes and surface morphologies.

Occurrence and significance: The triclinic system is common in minerals and organic crystals, often arising when no strong symmetry constraints are present during crystallization. It plays an important role in studying low-symmetry structures and in modeling materials that lack higher symmetry, such as certain organic crystals and some synthetic compounds.

Name and history: The term derives from Greek roots related to three angles or slopes, reflecting the oblique unit cell. The system was formalized in the 19th century as crystallography developed its taxonomy of crystal forms.