Basal twinning of Greenland corundum

• Published in: Mineralogy and Petrology
• Main Authors: Pignatelli, Isabella, Nespolo, Massimo, Pardieu, Vincent, Giuliani, Gaston, Morlot, Christophe
• Other Authors: Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Cristallographie, Résonance Magnétique et Modélisations (CRM2), Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), VP Consulting, Université Toulouse III Paul Sabatier - Faculté de médecine Purpan (UTPS), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT), Laboratoire Energies et Mécanique Théorique et Appliquée (LEMTA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2024
• Subjects: [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy; [CHIM.CRIS]Chemical Sciences/Cristallography; [SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography; Greenland
• Online Access: https://hal.univ-lorraine.fr/hal-04554326; https://doi.org/10.1007/s00710-024-00858-1

International audience Natural corundum shows two types of twins: “basal twin”, by reflection on (0003) pinacoid, very rare, and “rhombohedral twin”, by reflection on (1011), more frequent. The analysis of the structural continuity across the composition plane does not show any reason for a large difference in occurrence frequency, which is likely related to the limited development of the (0003) plane in the characteristic morphology of corundum. “Basal twins” occur with unusually high frequency in samples from Greenland, which also present an atypical platy morphology, where the (0003) face is well developed. This observation seems to confirm a morphological control on the occurrence of the “basal twin”. All analysed twinned samples show macrosteps on their pinacoidal faces and this feature has been related to the high-temperature conditions and intense fluid-rock interactions of Greenland deposit. This clearly suggests a strong relationship between the “basal twin” occurrence, the development of basal faces, and the formation conditions. However, due to the complex geological context and the different features of samples (e.g. two individuals with almost the same size versus several lamellae stacked along c axis), it is not possible to establish with certitude if the “basal twins” observed in Greenland samples are growth or mechanical twins.