The hydrothermal flow-through experiments of precipitation of silica minerals were conducted at 430°C and 31MPa. With increasing of the Al concentration in the input solution (0–6.7 ppm), the change of dominant precipitation of silica mineral was revealed such as amorphous silica → cristobalite → quartz, and the logarithmic precipitation rate increased linearly. The precipitation via nucleation is determined the third–order reaction. The rate equations of surface reaction and nucleation suggest that, for example, the dominant reaction is nucleation in the fracture of 0.1 mm width whereas it is surface reaction in the fracture of 0.01 mm width when the precipitation occurs from the solution of Ω = 2 at 200°C. This trend coincides with that the formation of blocky veins occurred in wider fractures comparatively in nature.
