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Monoclinic crystal system
From Wikipedia, the free encyclopedia
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 make an angle other than 90°.
Two monoclinic Bravais lattices exist: the simple monoclinic and the centered monoclinic lattices, with layers with a rectangular and rhombic lattice, respectively.
 Simple monoclinic |
 Centered monoclinic |
The crystal classes that fall under this crystal system are listed below, followed by their representations in international notation and Schoenflies notation, and mineral examples.
| Name | International | Schoenflies | Example |
|---|---|---|---|
| monoclinic normal |  |
C2h | gypsum, orthoclase, mica |
| monoclinic hemimorphic | 2 | C2 | halotrichite |
| monoclinic hemihedral | m | C1h | hilgardite |
The number of space groups for each crystal class is 6, 3, and 4, respectively.
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.
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., pp. 65 - 69, ISBN 0-471-80580-7