rhombohedral

In crystallography, the trigonal crystal system is one of the seven crystal systems. Sometimes the term rhombohedral lattice system is used as an exact synonym, whereas it is a subset. Crystals in the rhombohedral lattice system are always in the trigonal crystal system, but some crystals such as quartz are in the trigonal crystal system but not in the rhombohedral lattice system. The rhombohedral lattice system consists of the rhombohedral lattice, while the trigonal crystal system consists of the five point groups of the seven space groups with a rhombohedral lattice. There are 25 space groups whose point groups are one of the five in the trigonal crystal system, consisting of the seven space groups associated with the rhombohedral lattice system together with 18 of the 45 space groups associated with the hexagonal lattice system.

Das Trigonale Kristallsystem gehört zu den sieben Kristallsystemen in der Kristallographie. Es umfasst alle Punktgruppen mit einer  dreizähligen Dreh- oder Drehinversionsachse. Das trigonale Kristallsystem ist mit dem  hexagonalen Kristallsystem eng verwandt und bildet zusammen mit ihm die hexagonale Kristallfamilie.

Układ trygonalny – jeden z układów krystalograficznych.

Det trigonala kristallsystemet, tidigare det romboedriska kristallsystemet, är ett kristallsystem med tre av fyra axlar i ett plan.

В кристаллографии тригональная сингония — одна из семи сингоний. Определяется тремя базовыми векторами одинаковой длины, с равными, но не прямыми, углами между векторами.