Silicification of woods usually occur in terrestrial conditions, but sometimes it could be done in aquatic environments. Surface water silicification can be done through the precipitation of silica in silica-enriched hot springs. On the northern coast of central Japan, the Tateyama hot spring has a high silica content that contributes to the silicification of nearby fallen woods and organic materials. Silica precipitates rapidly out of the fluids and opal is the main form of silica. With a temperature of around 70°C and a pH value of around 3, the opal deposited is composed of silica spheres of different sizes arranged randomly.