We conducted general shear experiments on synthetic mixtures of quartz and muscovite aggregates at 800 °C and 1.5 GPa with 0.1 wt% H₂O added in the Griggs apparatus to investigate the role of muscovite content on the microstructural evolution and rheological properties of quartz aggregates. Muscovite content varied between 0, 5, 10 and 25% muscovite. Mechanically, the sample strengths ...