Monoclinic crystal system

File:Ortoclasio.jpgAn example of the monoclinic crystals, orthoclase

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 base. Hence two pairs of vectors are perpendicular, while the third pair make an angle other than 90°.

There exist two monoclinic Bravais lattices: the simple monoclinic and the centered monoclinic lattices, with layers with a rectangular and rhombic lattice, respectively.

* Simple monoclinic

Simple monoclinic

* Centered 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  | <math>\frac2m</math> | C2h | gypsum, orthoclase, mica
monoclinic hemimorphic  | <math>2</math> | C2 | halotrichite
monoclinic hemihedral  | <math>m</math> | 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.

## See also

[edit | edit source]

* Crystal structure

## References

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* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., pp. 65 - 69, ISBN 0-471-80580-7

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