CLASSIFICATION OF CRYSTALS 7 (The Monoclinic system)

6)    The Monoclinic System

Figure 35: The crystallographic axes of the monoclinic system

The Monoclinic system has the following characteristics;

-         3 crystallographic axes with unequal lengths intersecting at oblique angles.  That is a ≠ b ≠ c.

-         The a crystallographic axis is inclined towards the c crystallographic axis.  That is

-         Its axial angles are such that α = γ ≠ 90^o ≠ β

-         The unit form in this system is a solid with a rectangular prism and a rectangular base.

-         The diagnostic property of the monoclinic system is 1ⁱⁱ.

The monoclinic system has 3 classes as follows:

a)     The monoclinic holosymmetric (monoclinic prismatic) class

b)    The monoclinic hemimorphic (monoclinic sphenoidal) class

c)     The monoclinic clinohedral (monoclinic domatic) class

          The holosymmetric class of the system is the monoclinic holosymmetric (monoclinic prismatic) class with the following properties:

-         A center of symmetry

-         1 plane of symmetry

-         1 axis of symmetry; 1ⁱⁱ along the b crystallographic axis.

-         Examples include: gypsum, orthoclase, augite, hornblende, micas, epidote group and chlorite group.