In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base (a by b) and height (c), such that a, b, and c are distinct. All three bases intersect at 90° angles, so the three lattice vectors remain mutually orthogonal.
In two dimensions there are two orthorhombic Bravais lattices: primitive rectangular and centered rectangular. The primitive rectangular lattice can also be described by a centered rhombic unit cell, while the centered rectangular lattice can also be described by a primitive rhombic unit cell.
In three dimensions, there are four orthorhombic Bravais lattices: primitive orthorhombic, base-centered orthorhombic, body-centered orthorhombic, and face-centered orthorhombic.
|Standard unit cell|
|Right rhombic prism
In the orthorhombic system there is a rarely used second choice of crystal axes that results in a unit cell with the shape of a right rhombic prism; it can be constructed because the rectangular two-dimensional base layer can also be described with rhombic axes. In this axis setting, the primitive and base-centered lattices swap in centering type, while the same thing happens with the body-centered and face-centered lattices.
The orthorhombic crystal system class names, examples, Schönflies notation, Hermann-Mauguin notation, point groups, International Tables for Crystallography space group number, orbifold notation, type, and space groups are listed in the table below.
|#||Point group||Type||Example||Space groups|
|16-24||Rhombic disphenoidal||D2 (V)||222||222||[2,2]+||enantiomorphic||epsomite||P222, P2221, P21212, P212121||C2221, C222||F222||I222, I212121|
|25-46||Rhombic pyramidal||C2v||mm2||*22||||polar||hemimorphite, bertrandite||Pmm2, Pmc21, Pcc2, Pma2, Pca21, Pnc2, Pmn21, Pba2, Pna21, Pnn2||Cmm2, Cmc21, Ccc2
Amm2, Aem2, Ama2, Aea2
|Fmm2, Fdd2||Imm2, Iba2, Ima2|
|47-74||Rhombic dipyramidal||D2h (Vh)||mmm||*222||[2,2]||centrosymmetric||olivine, aragonite, marcasite||Pmmm, Pnnn, Pccm, Pban, Pmma, Pnna, Pmna, Pcca, Pbam, Pccn, Pbcm, Pnnm, Pmmn, Pbcn, Pbca, Pnma||Cmcm, Cmca, Cmmm, Cccm, Cmme, Ccce||Fmmm, Fddd||Immm, Ibam, Ibca, Imma|