triclinisch

Triclinisch, or the triclinic crystal system, is the least symmetric of the seven crystal systems used in crystallography. It is defined by a unit cell with three lattice vectors a, b, c that are generally of different lengths and three interaxial angles α, β, γ that are all oblique and not equal to 90 degrees. There are no constraints forcing equal axes or right angles, so triclinic crystals have the most general geometry among the crystal systems.

In terms of symmetry, the triclinic system exhibits very low symmetry. The point group is 1 or -1, and the Bravais lattice is primitive. Consequently, the space groups associated with the triclinic system are only P1 and P-1.

The lack of symmetry in the triclinic system has practical consequences: physical properties such as optical and thermal behavior are often highly anisotropic, varying with direction within the crystal. X-ray diffraction from a triclinic crystal yields a cell with all three edge lengths and all three angles being independent, requiring determination of the complete set a, b, c, α, β, γ.

Examples of minerals that crystallize in the triclinic system include several plagioclase feldspars, such as albite and anorthite. The system also describes many organic and inorganic crystalline materials where no higher symmetry is present. Overall, the triclinic system represents the most general and least symmetric framework used to classify crystalline substances.

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