Rapid wood silicification in hot spring water: an explanation of silicification of wood during the Earth's history

A hot spring water lake in Tateyama Hot Spring has a high content of silica and readily precipitates silica spheres and deposits of opal. Abundant fragments of naturally fallen wood impregnated with silica were found in the overflow stream of the lake. These silicifications resulted from the precipitation of silica spheres onto split surfaces or cell walls of the fallen wood. The textures of wood tissues are the same as those found on naturally silicified wood formed in the vicinity of volcanic regions in the geological record. These results explain the formation mechanism of certain naturally silicified wood fragments that seem to be formed under the same conditions as those found in the hot spring water. To confirm the silicification process, fresh wood pieces of alder wood ( Alnus pendula Matsumura) were placed in the hot spring water stream. Experimental wood fragments were silicified to nearly 40% by weight over a period of 7 years by the deposition of amorphous silica spheres in cell lumina of wood tissue. This study reveals that silicified wood can form under suitable conditions in time periods as short as tens to hundreds of years, and contributes to the understanding of the mechanisms forming silicified wood.