Crystal forms.

1. Crystal forms..Crystal forms..

2. Cube Cube
•general symbol is (100)
•Bounded by six similar faces, each parallel
to two of the axes.
•Each face is a square and interfacial
angles are 90 degree.
•The faces of the cube are parallel to the
principal or axial planes of symmetry.

3. Octahedron Octahedron
(111)(111)
•Is composed of eight equilateral triangular
faces, each of which intersects all three
crystallographic axes equally.
•Faces of the octahedron truncate
symmetrically the corners of the cube..

4. Rhomb-dodecahedron (110)Rhomb-dodecahedron (110)
•Composed of 12- rhomb shaped faces.
•Each face intersects two of the
crystallographic axes equally and is
parallel to the third.
•The faces of the dodecahedron truncate
the edges of both the cube and
octahedron.

5. Tetrahexahedron (hk 0)Tetrahexahedron (hk 0)
•Composed of 24 isosceles triangular
faces, each of which intersects one axis
at unity and the second at some multiple
and is parallel to the third.
•With respect to the inclination of their
faces different variety of tetrahedrons
observed.
•Most common one is (210)

6. Trapezohedron(hll)Trapezohedron(hll)
•24 trapezium shaped faces.
•Each of which intersect one of the
crystallographic axes at unity and the
other two at equal multiples.
•Some having different angles of
inclination.
•Most common is (211)
•Its also known as tetragon-trioctahedron.

7. Trisoctahedron (hhl)Trisoctahedron (hhl)
•Composed of 24 isosceles triangular
faces.
•Each of which intersects two of the
crystallographic axes at unity and the third
axis at some multiple.
•Face of which have different inclinations
but most common is (221)
•Also known as trigon-trioctahedron

8. Hexoctahedron (hkl)Hexoctahedron (hkl)
•Composed of 48 triangular faces
•Intersects all three crystallographic axes at
different lengths.
•Symbol is there for (321)
•Parametres are 1 a1, 3 a2, and 3/2 a 3.

9. Pyritohedron (hk0)Pyritohedron (hk0)
•Also called as pentagonal dodecahedron.
•Consist of 12 faces. Each of which
intersect one crystallographic axis at unity,
second axis at some multiple of unity and
parallel to the third.
•It is a typical form with the common
species, pyrite.

10. DiploidDiploid
•Bounded by 24 similar faces.
•Each meeting axes at unequal distances.
•Its general symbol is (hkl) I.e. (eg. 321)
•It’s also sometimes called
dyakisdodeahedron.

11. TetrahedronTetrahedron
•Bounded by four equilateral triangular
faces.
•Each of which intersects all
crystallographic axes at unit length.
•The tetrahedral form can be considered as
derived from the octahedron by omission
of the alternate faces and the extension of
the others.

12. Tristetrahedron (trigon- Tristetrahedron (trigon-
tritetrahedron)tritetrahedron)
•Form bounded by twelve like triangular
faces.
•Each face of the tetrahedron has been
raised to accommodate three others.
•Each face cuts two axes at equal length
and the third at a smaller length.
•General symbol (hll) eg. (211)

13. Deltoid- dodecahedronDeltoid- dodecahedron
•Also known as tetragon- tritetrahedron.
•This is a 12-faced form in which three
four-sided faces occur in place of one face
of the tetrahedron.
•Each faces cuts two axes at an equal
length and a third at a greater length. (hhl)
•Considered to be made up of the twelve
faces of the trisoctahedron that occur in
alternate octants.

14. HextetrahedronHextetrahedron
•It has 24 faces.
•Each face of tetrahedron has been raised
to accommodate six others.
•These corresponding to the faces of the
alternate octants of the hexoctahedron.
•General symbol is (hkl)