Crystallographic orientation and grain size data obtained by Electron Back Scatter Diffraction (EBSD) on quartz analysed in mylonitic quartzite from the Island of Elba (Italy).

Raw Electron Back Scatter Diffraction (EBSD) data on deformed quartz from a mylonitic quartzite sample of the Calamita Schists (Island of Elba, Italy) is available at https://doi.org/10.17632/8c937t6zs4.32. The investigated sample (IESP3SP78) was collected in quartz-rich outcrops exposed at the Praticciolo Cape and was used to realize an oriented thin section (cut parallel to lineation and perpendicular to foliation). Preliminary investigations were carried out by transmitted-light and scanning electron microscopy (SEM), in order to select key areas for EBSD analysis. EBSD mapping was performed on selected areas of deformed quartz, which was the only phase indexed and were processed to derive orientation maps, pole figures, inverse pole figures, misorientation axis distribution in sample and crystal coordinates. While the processed data is available on the original research article ("Fluid-assisted Strain Localization in Quartz at the Brittle/Ductile Transition"; https://doi.org/10.1029/2019GC008270), this contribution is devoted to supply the unprocessed EBSD data, together with a methodological description, aimed to allow the reproduction of the processed dataset. A brief statistical description of the investigated EBSD maps is also available. This data is valuable because it offers grain size and orientation analysis of deformed quartz investigated in a natural study case and the present publication makes it accessible to those working on naturally and experimentally deformed quartz.