General Description: The study, authored by Oretga-Arroyo and Pec. and submitted to Geophysical Research Letters explores the effect of particle size on the melting behavior of fault rocks. Verzasca Gneis granitoid powders ground using planetary ball milling are used in this study.This contribution includes the data used in their study as follows: GSD: The grain size distribution measurements of the various powders. DSC: Differential Scanning Calorimetry measurements of the various grain size distributions Optical Images: Document the samples before and after DSC measurements. Includes petrographic microscopy under plane (PPL) and cross (XPL) polarized light. SEM: Scanning electron photomicrographs. SEM: Raman Spectrosopy measurements of the samples pre and post DSC measurements.