Monoclinic crystal system

An example of the monoclinic crystals, orthoclase

In crystallography, the monoclinic crystal system is one of the seven lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic system. They form a rectangular prism with a parallelogram as its base. Hence two vectors are perpendicular (meet at right angles), while the third vector meets the other two at an angle other than 90°.

Bravais lattices and point/space groups 1
Crystal classes 2
Specific chemical examples 3
See also 4
References 5

Bravais lattices and point/space groups

Two monoclinic Bravais lattices exist: the primitive monoclinic and the centered monoclinic lattices, with layers with a rectangular and rhombic lattice, respectively.

Monoclinic Bravais lattice
Name	Primitive	Base-centered
Pearson symbol	mP	mC
Unit cell

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.

#	Point group					Type (Example)	Space groups
#	Name	Schoenflies notation (Schön.)	Hermann–Mauguin notation (Intl)	orbifold (Orb.)	Coxeter notation (Cox.)	Type (Example)	Space groups
3–5	Sphenoidal ^[2]	C₂	2	22	[2]⁺	enantiomorphic polar (halotrichite)	P2, P2₁ C2
6–9	Domatic ^[2]	C_1h (=C_1v = C_s)	2 = m	*11	[ ]	polar (hilgardite)	Pm, Pc Cm, Cc
10–15	Prismatic ^[2]	C_2h	2/m	2*	[2,2⁺]	centrosymmetric (gypsum)	P2/m, P2₁/m, C2/m P2/c, P2₁/c, C2/c

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.

Specific chemical examples

An example of a monoclinic crystal is elemental sulfur (which can also occur in a rhombic form).^[3]

References

^
^ ^a ^b ^c
^ C.Michael Hogan. 2011. . Encyclopedia of Earth, eds. A.Jorgensen and C.J.Cleveland, National Council for Science and the environment, Washington DCSulfur

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

The 7 crystal systems

triclinic monoclinic orthorhombic tetragonal trigonal hexagonal cubic (isometric)

Categories

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Monoclinic crystal system