the process by which silica minerals such as quartz, chalcedony, and opal fill pores or replace existing minerals, rock, or wood.

Silicification occurs in the earth’s interior through the action of hydrothermal (hot) and cold water saturated with silica. As aluminosilicate rock is weathered, a great deal of silica is freed and dissolves. Much of the dissolved silica is carried to the sea, but in places it moves downward and replaces various rock. Hydrothermally silicified carbonate rock is frequently associated with ores of mercury, antimony, and other nonferrous metals. At ordinary temperatures, loose rock on the bottom of lakes and seas is subject to silicification, as is solid rock; this occurs most frequently with limestones and dolomites, more rarely with clays and phosphorites. Accumulations of fine-grained quartz form when carbonate rocks are replaced, and aggregates of quartz and chalcedony develop when clayey rock is replaced. The presence of fine-grained quartz and quartz and chalcedony aggregates in ultrabasic rock indicates that deposits of silicate ores of nickel and cobalt may be found.

References in periodicals archive ?
The alteration of adjacent rocks within the deposits is relatively simple, and the alteration processes (Figure 7) mainly include dolomitization, calcitization, and pyritization, with silification and argillation also occurring over a smaller distribution range.
Wang, "Synthesis of PEOlated [Fe.sub.3] [O.sub.4] @Si[O.sub.2] nanoparticles via bioinspired silification for magnetic resonance imaging," Advanced Functional Materials, vol.
In this case, the silica saturates limestone layers or creates lenticular forms of silification, and--occasionally--hornstone forms.
Pedogenic silification of sedimentary rocks, such as sandstone and mudstone, during the Early Cretaceous has created the abundant, high quality material available at Quarry 35.
Since silification is the dominant alteration at Meikle, the majority of the ore is competent.
Grass leaf silification: natural selection for an inducible defense against herbivores.
Silification of carbonate pebbles in a fluvial conglomerate by ground water.
The mineralization process (ore development, calcitization, dolomitization and silification) resulted in the higher toughness of the rocks and in the lower porosity and absorbability.