Description: The angle between the twin plane and the basal pinacoid seem to be related to the composition but other factors distort the results when using this technique to identify different plagioclases. Mineral: Albite Description: Pericline law twin with rhombic section Location: Ritenbenk, Greenland Author: Böggild, 1805. In: V.M. Goldschmidt, Atlas der Krystallformen, 1913-1923 ('Feldspat-Gruppe. Albit'). System: Triclinic, point group: 1 Cell: a: 0.636, b: 1, c: 0.559, alpha: 94.33, beta: 116.56, gamma: 87.65 Image © Smorf

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