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Point Groups (Crystal Classes)

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Stereographic Projections Used to display crystal morphology. X for upper hemisphere. O for lower.

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Stereographic Projections We will use stereographic projections to plot the perpendicular to a general face and its symmetry equivalents (general form hkl). Illustrated above are the stereographic projections for Triclinic point groups 1 and -1.

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32 PointGroups: Hermann-Mauguin Symbols Three positions in H-M symbol Triclinic: No unique axis Only 1 or -1 Monoclinic: [010] Orthorhombic: [100], [010], [001] Tetragonal: [001], [100], [110] Trigonal: [001], [100], Hexagonal: [001], [100], [210] Cubic: [100], [111], [110]

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32 PointGroups (Crystal Classes) Triclinic: 1, 1 Monoclinic: 2, 2=m, 2/m Orthorhombic: 222, 2mm, 2/m2/m2/m (=mmm) Tetragonal: 4, 4, 4/m, 42m, 422 4mm 4/m2/m2/m Trigonal: 3, 3m, 32, 3, 32/m Hexagonal: 6, 6, 6/m, 6m2, 622, 6mm, 6/m2/m2/m Cubic: 23, 2/m3, 432, 43m, 4/m32/m

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Triclinic System

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Monoclinic System

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Orthorhombic System

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Trigonal System

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Tetragonal System

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Hexagonal System

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Cubic System

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32 PointGroups (Crystal Classes) Triclinic: 1, 1 Monoclinic: 2, 2=m, 2/m Orthorhombic: 222, 2mm, 2/m2/m2/m (=mmm) Tetragonal: 4, 4, 4/m, 42m, 422 4mm 4/m2/m2/m Trigonal: 3, 3m, 32, 3, 32/m Hexagonal: 6, 6, 6/m, 6m2, 622, 6mm, 6/m2/m2/m Cubic: 23, 2/m3, 432, 43m, 4/m32/m

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