romboedraalsed

Romboedraalsed, commonly referred to as rhombohedral, describe crystals and crystal structures whose basic repeating unit is a rhombohedron. This term is used in crystallography and mineralogy to characterize shapes and lattices where the unit cell is a skewed cube with parallelogram faces, giving rise to a distinctive threefold symmetry around a body diagonal.

In the conventional description, a rhombohedral lattice is defined by a = b = c and α = β = γ ≠ 90°. In many practical descriptions, especially for minerals, the rhombohedral character is represented using a hexagonal setting, where a ≈ b ≠ c and γ = 120°, with α = β = 90°. The system exhibits a threefold rotational symmetry along the principal axis and features rhombohedral cleavage in some minerals.

Common minerals with rhombohedral symmetry include calcite and dolomite, which exhibit rhombohedral crystal faces and characteristic cleavage patterns along rhombohedral planes. The rhombohedral description is also relevant for certain trigonal minerals and synthetic crystals that adopt this lattice arrangement.

Geometrically, a rhombohedron is a distorted cube with all edges of equal length but with oblique angles, producing six parallelogram faces. This shape underpins the naming and helps explain the optical and diffraction properties associated with rhombohedral crystals.

In summary, romboedraalsed refers to crystals and lattices with rhombohedral geometry, characterized by equal edge lengths and unequal, oblique angles, and it plays a key role in mineral identification, crystal habit analysis, and diffraction studies.