Talc, a hydrous magnesium silicate, is found in mafic or ultramafic rocks, where it is formed by hydration and/or silica metasomatism. Talc has attracted attention for its exceptional mechanical properties, which could explain the weakness of certain faults, such as the San Andreas fault. Talc is weaker than antigorite by a factor of ∼3–4 and weaker than chlorite by a factor of ∼2. Its coefficient of sliding friction (μ) ranges from 0.36–0.24 under dry conditions and is as low as 0.2 under wet conditions. This very low coefficient of friction has been attributed to weak bonding along basal (001) planes. However, beyond this simple consideration generally applicable to layered silicates, the mechanical properties and especially the deformation mechanisms of talc have been relatively little studied and are fairly poorly understood. In this study, we propose to utilize nanomechanical testing to investigate the plastic deformation mechanisms in talc single crystals under tension. We employ the PI-95 TEM Pico-indenter holder and the Push-to-Pull (PTP) device (Bruker, Inc.) to perform quantitative tensile tests at room temperature in situ in a Transmission Electron Microscope. The mechanical response of several single crystal specimens with various orientations of the basal (001) planes with respect to the tensile axis is investigated. It is observed that despite the presence of damage (nanovoids, nanocracks), talc does not exhibit brittle behaviour. Even when the orientation of the base planes induces very low resolved shear stress, the activation of dislocations is easy and leads to highly ductile behaviour. In the case where the basal plane is perpendicular to the tensile axis, talc undergoes deformation through amorphization. Atomic-scale calculations are presented to interpret this unexpected behaviour, based on molecular rearrangements triggered by dehydration.