it includes details about elements of crystals and unit cell explanation

1. SNPIT & RC
Presentation on: Elements of
crystal.
Subject: Geotechnics and
Applied Geology.(2130606)

2. Prepared By:
 Sindhvad Kathan = 160490106087
 Upadhyay Nishank = 160490106092
 Sharma Vishal = 160490106085
 Shukla Malhar = 160490106086

3. CRYSTAL
 A crystal may be defined as a natural solid body bounded by
smooth and plain surface. Arranged in an orderly (i.e.
geometrical) pattern , which is an outward expression of a
regular internal atomic structure.

4. ELEMENTS OF CRYSTAL
 Parts of crystal
 1. Angle
 2. Edge
 3. Face

5. 1. Crystal Faces
 The crystal are bounded by flat surfaces which are known as
faces.
 A crystal may have only two faces of the same geometrical
shape or it may have up to forty-eight faces of a combination
of geometrical shapes.

6. 2.Edge
 The line of intersection formed by any two adjacent faces in a
crystal is call an edge.

7. 3. Solid Angle
 The points of intersection formed by three or more adjacent
faces in a crystal are called solid angle.

8. 4. Interfacial Angle
 In a crystal, the angle between normal of two adjacent faces is
called ‘interfacial angle’ .
 Interfacial angles are measured either with a contact
goniometer or a reflecting goniometer.

9. Goniometer

10. 5. Distortion
 Inspite of perfect internal atomic arrangement, sometimes
crystals develop faces of different sizes shapes. This kind of
geometrical irregularity in the shape of crystal is called
‘distortion’.

12. 6.Simple form
 If a crystal is bounded by all similar or like faces, is called a
simple form.

13. Combination
 If a crystal is bounded by dissimilar or unlike faces, it is called
a combination. ( i.e. combination of different simple forms)

14. 7.Zone and zone axis
 In many crystals, a group of faces are arranged in such a
manner that their intersection edges are parallel to each other.
Such faces constitude a zone.
 A line which passes through the centre of the crystal and lie
parallel to the line of the faces intersections is called the zone
axis.

16. 8.Crystallographic Axes
 In order to describe the faces and symmetry of crystal, a set of
three or four reference axes are established. These imaginary
reference lines are called “crystallographic axes”.
 While fixing a crystal in its study position with reference to
the crystallographic axes, it is important to align it in such a
way that one of the axes runs front to back, from the observer,
another runs right to left, and one is passing from top to
bottom of the crystal.

17. Crystallographic
Axes

18. Axial Ratio
 It is the ratio between the lengths of different crystallographic
axes in a given crystal system and is always constant for that
crystal.
 Ex.:
a=10.47 A* a:b=10.47/12.87=0.813
b=12.87 A* b:c=12.87/24.49=0.525
c=24.49 A* a:c=10.47/24.49=0.4275

19. Unit Cell
 Unit cell is a tiny building block of crystal. Each crystal is
composed of number of a such unit cells. In each unit cell
there is a group of atoms linked in a fixed spatial relationship
to one another. Unit cell represent this smallest volume which
possesses all the chemical, phisical and geometrical properties
of the crystal different mineral species have different types of
unit cell.

20. 9.Symmetry
 The faces ,edges and solid angles in crystals occur with some
regularity. This is known as symmetry.
 Symmetry is property of fundamental importance for a crystal.
It can be studied with reference to three different characters,
commonly called elephants of symmetry. These are:
(i) Plane of symmetry
(ii) Axis of symmetry
(iii) centre of symmetry

21. (i) Plane of symmetry
 A plane of symmetry is an imaginary plane which divide a
crystal into two halves, each of which is the mirror image of
the other.

22. (ii) Axis of symmetry
 It is imaginary line through crystal about which if the crystal
is Rotated, it gives the observer exactly the same view more
than once in a single rotation.

23. (iii)Centre of symmetry
 A crystal is said to possess a centre of symmetry if on passing
an imaginary line from some definite face, edge or corner on
one side of crystal through its centre, another exactly similar
face, edge or corner is found on the other side at an equal
distance from the centre.
 The cube and octahedron possess a centre of symmetry,
whereas a tetrahedron does not. Many crystals have no planes
or axis of symmetry but do possess centre of symmetry.

24. THANK YOU