This ppt useful crystallography introduction

1. Crystallography and Mineralogy
Dr.B.GURUGNANAM
Professor and Head
Centre for Applied Geology
GRI-DU
Mr.K.KALAIVANAN
Research Scholar
Centre for Applied Geology
GRI-DU.

2. Introduction to Crystallography
What is crystallography?
CRYSTALLOGRAPHY is simply a fancy word
meaning "the study of crystals“
•The study of crystalline solids and the principles
that govern their growth, external shape, and
internal structure
•Crystallography is easily divided into 3 sections -
geometrical, physical, and chemical.

3. Definition of crystal
A CRYSTAL is a regular
polyhedral form, bounded by
smooth faces, which is assumed
by a chemical compound, due
to the action of its inter atomic
forces, when passing, under
suitable conditions, from the
state of a liquid or gas to that of
a solid.

4. Crystalline and Amorphous
• (In Greek amorphous means “formless”) do not have
overall regular internal structure; their constituent
particles are arranged randomly; hence, they are
isotropic, have no symmetry, and cannot be bounded by
faces.
• Particles are arranged in them in the same way as in
liquids; hence, they are sometimes referred to as super
cooled liquids.
• Examples of amorphous substances are glass, plastics.
• In distinction to crystalline substances, amorphous ones
have no clearly defined melting point.

5. Cont…
• Comparing curves of
cooling (or heating) of
crystalline substances and
amorphous substances, one
can see that the former has
two sharp bend-points (a
and b), corresponding to
the beginning and end
crystallization respectively,
whereas the latter is smooth
Curve of cooling of a crystalline
subsatnce
0
10
20
30
40
50
60
050100
time, min
To
a
b

6. Symmetry
Symmetry map be defined in rotation to
(i) Plane of symmetry
• Divided a crystal into two equal half
• Mirror plane
(ii) Axis of symmetry
• Parallel to the edge of intersection of two
crystal faces.
• Binary, trigonal, tetragonal, hexagonal
(iii) Centre of Symmetry
• Centre of symmetry if an imaginary line
passing the centre

7. Classification of crystals
• Classification of crystals according to the
degree of crystallization
•Euhedral crystals
•Subhedral crystals
•Anhedral crystals
Euhedral Crystal Subhedral Crystal Anhedral
Crystal

8. Crystallographic forms
1- Pedion
It is an open form made up of a single face

9. Cont…
1- Pinacoid
It is an open form made up of two parallel faces
Basal Pinacoid
Side
pinacoid
Front Pinacoid

10. Cont…
3- Dome
It is an open form made up of two
nonparallel faces symmetrical with
respect to a symmetry plane
4- Sphenoid
It is an open form made up of
two nonparallel faces
symmetrical with respect to a 2-
fold or 4-fold symmetry axis

11. Cont…
5- Disphenoid
It is an closed form composed of a four-faced form in
which two faces of the upper sphenoid alternate with
two of the lower sphenoid.

12. Cont…
6-Bipyramid
It is an closed form composed of 3, 4, 6,
8 or 12 nonparallel faces that meet at a
point
Orthorhombic bipyramed
Ditetragonal bipyramid
Tetragonal bipyramid
Dihexagonal bipyramid
Hexagonal bipyramid

13. Cont…
7- Prism
It is an open form composed of 3, 4, 6, 8 or 12 faces, all of which
are parallel to same axis.
Orthorhombic prism Tetragonal prism
Ditetragonal prism
Hexagonal prism
Dihexagonal prism

14. Cont…
8- Rhombohedron
It is an closed form composed of
6 rhombohedron faces,
9- Scalenohedron
It is an closed form composed of 12
faces, each face is a scalene triangle.
There are three pairs of faces above and
three pairs below in alternating
positions

15. Crystal Habits
The term "crystal habit" is used to categorize
the appearance, shape, and size of a crystal, and
identify its unique growth characteristics that
result from its crystalline structure and growth
environment.
1. Crystal Twinning ( two individual crystals share some of
the same crystal lattice points)
2. Growth Conditions (heat, pressure, and space)
3. Trace Impurities (present during crystal formation)

17. Crystal Habits

18. Crystal Habits

19. Crystal Habits

20. Crystal Habits

21. Crystal Habits

22. Crystal Habits

23. Crystal Habits

24. Crystal Habits