In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a parallelogram as its base. Hence two pairs of vectors are perpendicular, while the third pair makes an angle other than 90°.
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Bravais lattices and point/space groups
Two monoclinic Bravais lattices exist: the simple monoclinic and the centered monoclinic lattices, with layers with a rectangular and rhombic lattice, respectively.
 Simple monoclinic (P) |
 Centered monoclinic (C) |
Crystal Classes
The monoclinic crystal system class names, examples, Schönflies notation, Hermann-Mauguin notation, point groups, International Tables for Crystallography space group number[1], orbifold, type, and space groups are listed in the table below.
| Crystal Class | Example | Schönflies | Hermann-Mauguin notation | point groups | # | orbifold | Type | space groups | |||||||
| Sphenoidal [2] | halotrichite | C2 |  |
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3-5 | 22 | enantiomorphic polar |  |
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| Domatic [2] | hilgardite | C1h (=C1v = Cs) | m |  |
6-9 | 1* | polar |  |
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| Prismatic [2] | gypsum | C2h |  |
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10-15 | 2* | centrosymmetric |  |
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Wolframite, Gypsum, Sphene, Augite and Orthoclase
Sphenoidal is also monoclinic hemimorphic; Domatic is also monoclinic hemihedral; Prismatic is also monoclinic normal.
The three monoclinic hemimorphic space groups are as follows:
- a prism with as cross-section wallpaper group p2
- ditto with screw axes instead of axes
- ditto with screw axes as well as axes, parallel, in between; in this case an additional translation vector is one half of a translation vector in the base plane plus one half of a perpendicular vector between the base planes
The four monoclinic hemihedral space groups include
- those with pure reflection at the base of the prism and halfway
- those with glide planes instead of pure reflection planes; the glide is one half of a translation vector in the base plane
- those with both in between each other; in this case an additional translation vector is this glide plus one half of a perpendicular vector between the base planes.
See also
References
- ^ Prince, E., ed (2006). International Tables for Crystallography. International Union of Crystallography. doi:. ISBN 978-1-4020-4969-9.
- ^ a b c "The 32 crystal classes". http://www.cartage.org.lb/en/themes/sciences/physics/SolidStatePhysics/AtomicBonding/CrystalStructure/32Crystal/32Crystal.htm. Retrieved on 2009-07-08.
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., pp. 65 - 69, ISBN 0-471-80580-7
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