rhombic

Rhombic is an adjective derived from the rhombus, a parallelogram with four equal sides. In geometry, a rhombus has opposite sides parallel and opposite angles equal; its diagonals intersect at right angles and bisect the vertex angles, and the figure is a square only if all angles are 90 degrees. The term rhombic is often used to describe shapes, tilings, or symmetries that resemble or are built from rhombi.

In geometry and related fields, rhombic descriptions appear in tilings and polyhedra. A rhombic tiling covers the plane with rhombi (diamonds) without gaps or overlaps, and a rhombic dodecahedron is a polyhedron with twelve rhombic faces. The common notion is that rhombic elements exhibit equal side lengths and a diamond-like, or rhombus-based, geometry.

In crystallography and mineralogy, rhombic has historical usage to denote certain lattice types with rhombus-like symmetry. The rhombohedral lattice, derived from the trigonal crystal system, is described by a rhombohedron primitive cell, while the orthorhombic system is sometimes referred to in older texts as rhombic. Modern terminology distinguishes orthorhombic and rhombohedral structures to avoid ambiguity. A well-known example is rhombic sulfur, the orthorhombic allotrope stable at room temperature, where the crystal arrangement yields a rhombus-based lattice.

In summary, rhombic describes objects or structures that feature rhombi or rhombus-like symmetry, spanning geometry, tilings and polyhedra, and extending into historical crystallography usage.