Trikliininen

Trikliininen, in crystallography and mineralogy, refers to the triclinic crystal system. It is the least symmetric of the seven crystal systems. Crystals of this system have unit cells in which all three axes are of different lengths (a ≠ b ≠ c) and all three interaxial angles are unequal and not equal to 90° (α ≠ β ≠ γ and α, β, γ ≠ 90°).

Because of this geometry, triclinic crystals typically lack rotational, mirror, and glide symmetries; the only symmetry available in the primitive case is the identity, and in the centrosymmetric variant is a center of inversion.

The triclinic system has two Bravais lattices: primitive (P) and centrosymmetric (P-1). Corresponding space groups are P1 and P-1, among the 230 space groups in crystallography, representing minimal symmetry.

In practice, triclinic crystals are noted for their low symmetry, complex diffraction patterns, and often pronounced distortions. Determination of their structure by X-ray or neutron diffraction requires careful data collection and refinement, as symmetry constraints are weak and many parameters must be solved.

The term "trikliininen" is used in Finnish-language literature to describe materials belonging to this crystal system. The concept is also described in English-language crystallography as triclinic, with examples in natural minerals and synthetic compounds joining a wide range of chemical compositions.