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SYMMETRY OF MATTER
Lesson 5 - Page 2

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Seven Crystalline Structures

definition

Triclinic - requires either a center or only translational symmetry.  Angles are all different

Monoclinic - 1 two fold axis of rotation or 1 mirror plane

Orthorhombic - requires either 3 two fold axis of rotation or 1 two fold axis of rotation and two mirror planes. 

Hexagonal  - 6 part symmetry (one 6 fold);  all sides are not equal; 60E angles

Rhombohedral or Trigonal  - requires 1 three fold axis of rotation

Tetragonal  -  has 2 sides the same and one side different, at 90Eangles requires 1 four fold axis of rotation. 

Cubic or Isometric  - 4 three fold axis of rotationAll sides are equal with 90E angles

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