In geology, silicification is a process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and abundant compound found in organic and inorganic materials, including Earth's crust and mantle. There are a variety of silicification mechanisms. In silicification of wood, silica permeates into and occupies cracks and voids in wood such as vessels and cell walls. The original organic matter is retained throughout the process and will gradually decay through time. In the silicification of carbonates, silica replaces carbonates by the same volume. Replacement is accomplished through the dissolution of original rock minerals and the precipitation of silica. This leads to a removal of original materials out of the system. Depending on the structures and composition of the original rock, silica might replace only specific mineral components of the rock. Silicic acid (H4SiO4) in the silica-enriched fluids forms lenticular, nodular, fibrous, or aggregated quartz, opal, or chalcedony that grows within the rock. Silicification happens when rocks or organic materials are in contact with silica-rich surface water, buried under sediments and susceptible to groundwater flow, or buried under volcanic ashes. Silicification is often associated with hydrothermal processes. Temperature for silicification ranges in various conditions: in burial or surface water conditions, temperature for silicification can be around 25°−50°; whereas temperatures for siliceous fluid inclusions can be up to 150°−190°. Silicification could occur during a syn-depositional or a post-depositional stage, commonly along layers marking changes in sedimentation such as unconformities or bedding planes.
- ⭐ Core Definition: Silicification
- Silicification in the context of Sarsen
- Silicification in the context of Agate
- Silicification in the context of Petrified forest, Khorixas
Silicification in the context of Sarsen
Sarsen stones are silicified sandstone blocks found extensively across southern England on the Salisbury Plain and the Marlborough Downs in Wiltshire; in Kent; and in smaller quantities in Berkshire, Essex, Oxfordshire, Dorset, and Hampshire.
View the full Wikipedia page for SarsenSilicification in the context of Agate
Agate (/ˈæɡɪt/ AG-it) is a variously translucent, banded variety of chalcedony. Agate stones are characterized by alternating bands of different colored chalcedony and may also include visible quartz crystals. They are common in nature and can be found globally in a large number of different varieties. There are some varieties of chalcedony without bands that are commonly called agate (moss agate, fire agate, etc.); however, these are not true agates. Moreover, not every banded chalcedony is an agate; for example, banded chert forms via different processes and is opaque. Agates primarily form as nodules within volcanic rock, but they can also form in veins or silicified fossils. Agate has been popular as a gemstone in jewelry for thousands of years, and today it is also popular as a collector's stone. Some duller agates sold commercially are artificially treated to enhance their color.
View the full Wikipedia page for AgateSilicification in the context of Petrified forest, Khorixas
The Petrified forest, located 42 kilometres (26 mi) west of the Namibian town of Khorixas, on the C39 road, is a deposit of large tree trunks that have "turned to stone" through a process of diagenesis. There are at least two large tree trunks, each 45 metres (148 ft) long, exposed to view. Several hundred others are located in the vicinity.
It is believed that the trees were swept downstream by a large flood and covered by alluvial sands. Deprived of air, the organic matter could not rot and decay, but instead, over millions of years, underwent silicification, whereby each cell is individually fossilised and the appearance, if not the colour, of wood is retained. The surrounding sands became sandstone, which is now eroding away.
View the full Wikipedia page for Petrified forest, Khorixas