• Chlorite, amphibole, and altered plagioclase are highly microwave-sensitive, showing rapid heating (>2.5 °C/s) and violent rupture.
• Surface temperature non-uniformity (VT) evolves through increasing, decreasing, and stabilizing phases, reflecting heat accumulation and transfer dynamics.
• Temperature gradients spatially correlate hotspots with rupture points, with shallow melting affecting surface temperature distribution.
• Findings enable prediction of microwave heating in hard rocks and deepen understanding of microwave-induced weakening mechanisms.