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GY 302: Crystallography &
Mineralogy
GY 302: Crystallography &
Mineralogy
UNIVERSITY OF SOUTH ALABAMA
Lecture 2: More Symmetry
Operations, Bravais Lattices
Lecture 2: More Symmetry
Lecture 2: More Symmetry
Operations, Bravais Lattices
Operations, Bravais Lattices
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±
±
A long winded introduction
A long winded introduction
±
±
Introduction to crystallography
Introduction to crystallography
±
±
Symmetry
Symmetry
Crystal Systems
The 6 (or 7) Crystal Systems.
Plagioclase
"
≠
$
≠
(
≠
90°
a
≠
b
≠
c
Triclinic
6
Gypsum, Orthoclase
"
=
$
=90° ,
(
≠
90°
a
≠
b
≠
c
Monoclinic
5
Aragonite, Staurolite
"
=
$
=
(
=90°
a
≠
b
≠
c
Orthorhombic
4
Quartz, Calcite
"
=
$
=120° ,
(
=90°
a= a
1
=b
≠
c
Trigonal
3b
Apatite
"
=
$
=120° ,
(
=90°
a
1
= a
2
=a
3
≠
c
Hexagonal
3a
Zircon
"
=
$
=
(
=90°
a = b
≠
c
Tetragonal
2
Halite, Galena, Pyrite
"
=
$
=
(
=90°
a = b = c
Cubic
1
Mineral examples
Angles between axes
Axes
Crystal System
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In order to fully understand how crystals are “put together”, We
need to reconsider symmetry.
In the last lab, we examined 3 symmetry operations:
1)
Reflection
(mirror planes)
Crystal Systems
In order to fully understand how crystals are “put together”, We
need to reconsider symmetry.
In the last lab, we examined 3 symmetry operations:
1) Reflection (mirror planes)
2) Rotation
(2, 3, 4, 6 fold axes)
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There are two other operations that we did not have a chance to
discuss at the start of lab 1 (e.g., rotoinversion)
1) Reflection (mirror planes)
2) Rotation (2, 3, 4, 6 fold axes)
3)
Inversion
Center of
Inversion
Crystal Systems
1) Reflection (mirror planes)
2) Rotation (2, 3, 4, 6 fold axes)
3)
Inversion
4)
Translation
5) Screw Rotation
6) Glide Rotation
7) Rotoinversion
Basic symmetry
operations
Compound symmetry
operations
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1.
Rotoinversion
2.
Translational Symmetry
3.
Bravais Lattices
Symmetry in Crystals
Rotation axes:
http://www.cartage.org.lb
2fold Rotation Axis
 If an object appears
identical after a rotation of 180
o
, that is twice in a
360
o
rotation, then it is said to have a 2fold
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This note was uploaded on 02/05/2012 for the course GLY 302 taught by Professor Staff during the Spring '11 term at S. Alabama.
 Spring '11
 Staff

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