1. PYRITOHEDRAL CLASS- 3Aii, 4Aiii, 3P, C
TYPICAL FORMS OF THIS CLASS ARE PYRITOHEDRON (PENTAGONAL
DODECAHDERON) AND THE DIPLOID (Dyakisdodecahedron)
1) PYRITOHEDRON:
• Type mineral pyrite.
• Bounded by 12faces.
• General symbol is (hk0) and is related to tetrahexahedron.
• Positive- if the long axis is vertical; Negative- if the long axis is horizontal.
2 ) DIPLOID:
• Bounded by 24faces, the faces are quadrilaterals or trapeziums.
• General symbol is (321) and is derived from hexoctahedron.
TETRAHEDRAL CLASS- 3A ii, 4A iii, 6P.
1) TETRAHEDRON:
• Bounded by four faces (equilateral triangle)
• General symbol is (111)
• The principal axes join the centres of the opposite edges.
• Developed from alternate octants of octahedron.
• Hemihedral form of octahedron
• Positive and negative forms are present .
2) DELTOID- Dodecahedron:
Bounded by 12 faces, each a quadrilateral, having miller indices as (221)
Also known as tetragonal tristetrahedron ad is a hemihedral form of Trisoctahedron.
3) TRIGONAL TRIS TETRAHEDRON.
• It has the general symbol (hll) and is bounded by 12 like triangular faces.
Developed from trapezohedron.
4) HEXTETRAHEDRON:
• Bounded by 24 scalene triangular faces.
• General symbol is (hkl)
• It is developed from Hexoctahedron.
PRISM:
Prisms, in systems other than the isometric, have been defined to be forms whose faces
are parallel to the vertical axis of the crystal while they meet the horizontal axes.
TETRAGONAL SYSTEM: - three types of prism depends on the number of faces and
the orientation.
• I-Order Prism- four faced form parallel to C- axis, general symbol is (110)
• II-Order Prism- four faced form parallel to C- axis, general symbol is (100)
• Ditetragonal prism- 8 faced form parallel to C- Axis, general symbol is (210)
• Third order prism- tripyramidal class,

2. Hexagonal system:
• I-Order Prism- includes six faces , each one of which is parallel to C- axis, meets
two adjacent horizontal axes at equal distance, while it is parallel to the third
horizontal axis.general symbol is (10-1 0)
• II-Order Prism- includes six faces , each one of which is parallel to C- axis, meets
the three horizontal axes, last named axis at unit distances and the others at
double this distances..general symbol is (11-20)
• Dihexagonal prism- 12 faced form parallel to C- Axis, general symbol is (hk_i 0)
• Third order prism- tripyramidal class,
ORTHORHOMBIC SYSTEM: