Common minerals : Diopside, Hedenbergite, Augite etc.

• Crystallographic axis : a  ≠ b ≠  c , a^b = 90^o, b^c = 90^o, a^c ≠ 90^o
  • where,
  • c = vertical axis, b = ortho axis, a = clino axis
• Characteristic Symmetry elements :

Classes of the System

1. Normal class / Gypsum type (a : b : c = 0.69 : 1 : 0.41, β = 80^o42′)
   • Plane of Symmetry : 1
   • Axis of Symmetry : 1 axis of 2 fold
   • Centre of Symmetry : Present
2. Hemimorphic class/ Tartric acid type
   • Plane of Symmetry : no
   • Axis of Symmetry : 1 axis of 2 fold
   • Centre of Symmetry : no
3. Clinohedral class/ Clinohedrite type
   • Plane of Symmetry : 1
   • Axis of Symmetry : no
   • Centre of Symmetry : no

Unit forms of Normal class :

Form	No. of faces	Miller Indices
Basal pinacoid ‘c’ pinacoid	2	001
‘a’ pinacoid Front pinacoid Ortho pinacoid	2	100
‘b’ pinacoid Side pinacoid Clino pinacoid	2	010
Prism	4	110
Hemi macrodome	02 (2)	101
Clinodome	4	011
Hemi pyramid	4 (2)	hkl (111)