![]() Over time, almost all the original organic material is lost only around 10% remains in the petrified wood. ![]() Thus silicification begins within the cell walls, and the spaces within and between cells are filled with silica more gradually. Additional silica then replaces the cellulose as it decomposes, so that cell walls are often preserved in great detail. Silica binds to the cellulose in cell walls via hydrogen bonding and forms a kind of template. Calcite and pyrite are much less common, and others are quite rare. Some 40 minerals have been identified in petrified wood, but silica minerals are by far the most important. Non-mineralized fossil wood is rapidly destroyed when exposed by erosion, but petrified wood is quite durable. The petrified wood is later exposed by erosion of surrounding sediments. Non-mineralized wood has been recovered from Paleozoic formations, particularly Callixylon from Berea Sandstone, but this is very unusual. The wood is then mineralized to transform it to stone. Wood is preserved from decomposition by rapid entombment in mud, particularly mud formed from volcanic ash. In addition to microbial decomposition, wood buried in an alkaline environment is rapidly broken down by inorganic reactions with the alkali. As a result, fossil wood older than Eocene (about 56 million years old or older) has lost almost all its holocellulose, and only lignin remains. ![]() The rate of decay is affected by temperature and moisture content, but exclusion of oxygen is the most important factor preserving wood tissue: Organisms that decompose lignin must have oxygen for their life processes. The lignin is hydrophobic (water-repelling) and much slower to decay. ĭead wood is normally rapidly decomposed by microorganisms, beginning with the holocellulose. The hemicellulose and lignin encrust and reinforce the cellulose microfibrils. ![]() Hemicellulose, a branched polymer of various simple sugars, makes up the majority of the remaining composition of hardwood while lignin, which is a polymer of phenylpropanes, is more abundant in softwood. Cellulose is composed of long chains of polymerized glucose arranged into microfibrils that reinforce the cell walls in the wood. Almost half of this is cellulose, which gives wood much of its strength. Together, these substances make up 95% of the dry composition of wood. Wood is composed mostly of holocellulose ( cellulose and hemicellulose) and lignin. The lack of oxygen slows decay of the wood, allowing minerals to replace cell walls and to fill void spaces in the wood. Petrified wood forms when woody stems of plants are buried in wet sediments saturated with dissolved minerals. The blue-green stains are from oxidation of the chalcocite to azurite and malachite. The black wood at left shows unusual mineralization with chalcocite and other sulfide minerals. The brown wood at right shows conventional silica mineralization. Petrified wood from the Shinarump Formation at the Nacimiento Mine, Cuba, New Mexico. A forest where such material has petrified becomes known as a petrified forest. However, petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains or volcanic lahars and ash beds. ![]() Silica in the form of opal-A, can encrust and permeate wood relatively quickly in hot spring environments. Most of the organic matter often decomposes, however some of the lignin may remain. There needs to be a balance between the decay of cellulose and lignin and mineral templating for cellular detail to be preserved with fidelity. During replacement, the plant's cell walls act as a template for mineralization. Mineral-laden water flowing through the sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. The petrifaction process occurs underground, when wood becomes buried in water or volcanic ash. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. In some instances, the original structure of the stem tissue may be partially retained. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal, chalcedony, or quartz). Petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement. Petrified wood, also known as petrified tree (from Ancient Greek πέτρα meaning 'rock' or 'stone' literally 'wood turned into stone'), is the name given to a special type of fossilized wood, the fossilized remains of terrestrial vegetation. Petrified log at the Petrified Forest National Park ![]()
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