Description: Mineral: Tetrahedrite Description: Penetration twin on [111] Location: Cavnic (Kapnik), Romania Author: C. Palache, H. Berman, C. Frondel, The system of mineralogy. Vol I, 7th edition, John Wiley & Sons, New York, 1944. System: Cubic, point group: 43m Cell: a: 1, b: 1, c: 1, alpha: 90, beta: 90, gamma: 90 image & data © Smorf This one is clearly a Penetration twin on [111], with 60º rotation around [111] as a twin operation. Why the previous twin have the same name?

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