Twinning_F11

Twinning_F11 - Twinning GLY 4200 Twinning, 2011 1 Twinning...

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1 Twinning GLY 4200 Twinning, 2011
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2 Twinning Illustration The twin plane cannot be a part of the normal symmetry of a crystal
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3 Twinning Operations Reflection across a mirror plane. The added mirror plane would then be called a twin plane Rotation about an axis or line in the crystal. The added rotation axis would then be called a twin axis Inversion through a point. The added center of symmetry would then be called a twin center
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4 Twin Law Must define two things: The type of twin operation The orientation of the twin element associated with the operation
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5 Types of Twinning Twins may also be classified on the basis of their physical properties There are two basic types of twin Contact twins Penetration twins
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6 Contact Twinning Have a planar composition surface separating two individual crystals These are usually defined by a twin law that expresses a twin plane Orthoclase twinned on the Braveno Law
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7 Polysynthetic Twinning A type of multiple contact twinning is called polysynthetic The compositions surfaces are parallel to one another, they are called polysynthetic Plagioclase commonly shows this type of twinning, called the Albite Twin Law, with {010} as the twin plane Such twinning is one of the most diagnostic features of plagioclase
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8 Cyclic Twinning Another type of contact twinning If the composition surfaces are not parallel to one another, they are called cyclical twins Shown here is the cyclical twin that occurs in chrysoberyl
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Twinning_F11 - Twinning GLY 4200 Twinning, 2011 1 Twinning...

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