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 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 |
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 |
| monoclinic hemimorphic |
2 |
C2 |
|
| monoclinic hemihedral |
m |
C1h |
sucrose |
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
