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Moelo, Y., Nespolo, M. & Farges, F. (2023) Pyrite contact twins. Acta Crystallographica Section B-Structural Science Crystal Engineering and Materials, 79 32–45. 
Added by: Richard Baschera (2023-03-24 13:52:30)   Last edited by: Richard Baschera (2023-03-24 13:59:08)
Type de référence: Article
DOI: 10.1107/S2052520622011714
Clé BibTeX: Moelo2023
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Catégories: IMN
Créateurs: Farges, Moelo, Nespolo
Collection: Acta Crystallographica Section B-Structural Science Crystal Engineering and Materials
Consultations : 31/148
Indice de consultation : 36%
Indice de popularité : 9%
Résumé     
Two examples of contact twins in pyrite from Peru are described. The first one, from Pasto Bueno ore deposit, shows the pyritohedron {120} as principal form, accompanied by the {111} octahedron and {100} cube as secondary forms, giving a lenticular aspect. (111) is the composition plane, and the twin operation is any one of the three binary axes < 110i > within this plane. The second one (unknown ore deposit) presents two forms, the octahedron {111} and the pyritohedron {120}; the two crystals in the twin are elongated along {[}101] and {[}011], respectively, producing a V profile. It is a reflection twin where the twin plane (110) coincides with the composition plane. These twins are by merohedry. Another contact twin is known in the literature, reported by Gaubert {[}Bull. Soc. Fr. Mine ` ral. Cristallogr. (1928), 51, 211-212] who described it as a spinel twin, i.e. a reflection twin with twin and composition plane (111); here it is shown that it is actually a rotation twin in which the twin operation is a 180 degrees rotation about any of the three equivalent directions < 211 >, contained in the (111) composition plane. The occurrence of these twins as well as the doubtfulness of the spinel twin in pyrite shows a direct relationship with the structural interpretation based on the pseudo-symmetry of the crystallographic orbits.
  
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