Laser confocal microscopy with differential interference contrast microscopy (LCM-DIM) was used to study in situ the biotite (001) basal surface dissolution performing long-term flow-through experiments at pH 1 (T = 11.5−70 °C). Time-lapse image sequences of large areas (up to 1 mm) of the evolving cleavage (001) surface showed that dissolution only occurs at surface edges. In addition, in contrast to an observed rapid dissolution at low steps (few layers), swelling and contraction of the edge layers occurred at high steps (many layers). An increase in temperature enhanced the surface edge dissolution from 7.5 × 10 −4 μm s −1 at 11.5 °C to 6.2 × 10 −2 μm s −1 at 70 °C. The results obtained in this work demonstrate that LCM-DIM is a powerful technique to study in situ the dissolution mechanism and kinetics of phyllosilicates.