Orthorhombic crystal system explained

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.

Bravais lattices

There are four orthorhombic Bravais lattices: primitive orthorhombic, base-centered orthorhombic, body-centered orthorhombic, and face-centered orthorhombic.

For the base-centered orthorhombic lattice, the primitive cell has the shape of a right rhombic prism;^[1] it can be constructed because the two-dimensional centered rectangular base layer can also be described with primitive rhombic axes. Note that the length

a of the primitive cell below equals (1)/(2) \sqrt{a ^{2+b} ^{2}} of the conventional cell above.

Crystal classes

The orthorhombic crystal system class names, examples, Schönflies notation, Hermann-Mauguin notation, point groups, International Tables for Crystallography space group number,^[2] orbifold notation, type, and space groups are listed in the table below.

	Point group					Type	Example	Space groups
Name^[3]	Schön.	Intl	Orb.	Cox.	Primitive			Base-centered	Face-centered	Body-centered
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	[2]	Polar	Hemimorphite, bertrandite	Pmm2, Pmc<	-- not a PMCID-->21, 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

In two dimensions

See main article: Rectangular lattice. In two dimensions there are two orthorhombic Bravais lattices: primitive rectangular and centered rectangular.

See also

• Crystal structure
• Crystal system
• Overview of all space groups

Further reading

• Book: Hurlbut. Cornelius S.. Klein. Cornelis. 1985. Manual of Mineralogy. 20th. 69–73. 0-471-80580-7. registration.
• Book: Hahn. Theo. International Tables for Crystallography, Volume A: Space Group Symmetry. International Tables for Crystallography. Springer-Verlag. Berlin, New York. 5th. 978-0-7923-6590-7. 10.1107/97809553602060000100. 2002. A.

Notes and References

1. See, row oC, column Primitive, where the cell parameters are given as a1 = a2, α = β = 90°
2. Book: International Tables for Crystallography . 10.1107/97809553602060000001 . 978-1-4020-4969-9 . E. . Prince . 2006 . International Union of Crystallography. 146060934 .
3. Web site: The 32 crystal classes . 2018-06-19.