rhombohedrischen

Rhombohedrischen refers to the rhombohedral order, geometry and lattice concepts that are based on rhombohedra, a class of polyhedra whose faces are rhombi. In geometry, a rhombohedron is a six-faced figure with opposite faces parallel and all edges of equal length in many realizations; the angles between edges are not necessarily right angles.

In crystallography, rhombohedral describes a crystal system or lattice that exhibits rhombohedral symmetry. The unit cell of this system can be a rhombohedron, which is a special parallelepiped with equal edge lengths and oblique angles. In practice, the rhombohedral system is often described using a hexagonal setting for trigonal crystals, reflecting threefold rotational symmetry around a vertical axis. This dual description means some minerals are classified as trigonal or hexagonal in common parlance, while the underlying lattice has rhombohedral characteristics.

Two related concepts are important: the rhombohedral lattice (sometimes called the "R" or primitive rhombohedral lattice) and the broader trigonal (threefold) crystallography. In modern terminology, many minerals that were once labeled strictly as rhombohedral are now discussed in the context of the trigonal crystal system, though their unit cells can retain rhombohedral geometry.

Examples frequently cited in the context of rhombohedral crystals include calcite, which forms rhombohedral crystals, illustrating how the rhombohedrischen concept manifests in natural minerals. The term is used in mineralogy, crystallography and geometry to describe shapes, lattices and symmetry related to rhombus-based polyhedra.