Abstract The diffusivity and diffusion mechanisms of hydrogen together with deuterium lithium, parallel to the c axis quartz, were investigated experimentally at 800°C, 0.1 GPa activity H 2 O or ≈ 1 [ is used throughout this work describe rather than D, avoid confusion coefficient, D ]. pH was set using mixtures (or O) HCl. Three types experiment conducted: (1) H-in/Li-out; (2) H-in/H-out; (3) ...