# Symmetry and stereonets - PowerPoint PPT Presentation

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Symmetry and stereonets. Point symmetry: 32 possible combinations Mirrors, rotation, center of symmetry, rotoinversion 6 crystal systems. 6 crystal systems C-axis has highest rotation or longest growth direction All axes have + and - ends. Stereonets . 3-D projection into 2-D. stereonets.

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Symmetry and stereonets

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## Symmetry and stereonets

• Point symmetry: 32 possible combinations

• Mirrors, rotation, center of symmetry, rotoinversion

• 6 crystal systems

• 6 crystal systems

• C-axis has highest rotation or longest growth direction

• All axes have + and - ends

### Stereonets

• 3-D projection into 2-D

### stereonets

• Have on them

• crystal axes

• Crystal faces

• Symmetry elements

### How to plot crystal faces

• Orient block on stereonet

• Faces in northern hemisphere are X’s

• Faces in southern hemisphere are O’s

• Plotting poles to faces (line perpendicular to the crystal face)

• Faces in center are horizontal

• Faces on edge are vertical

• Faces in between are at an angle

### How to plot symmetry elements on stereonet

• Mirror planes are solid lines

• Dashed lines are axes of rotation with no mirror

• Use symbols for rotations