Petrified wood

thumb|upright=1.15|Polished slice of a petrified tree from the [[Late Triassic Period (approximately 230 million years ago) found in Arizona. The remains of insects can be detected in an enlarged image.]]

thumb|Petrified log at the [[Petrified Forest National Park]]

Petrified wood is the name given to a special type of fossilized wood, the fossilized remains of terrestrial vegetation. Petrifaction (from Ancient Greek meaning 'rock' or 'stone'), is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal, chalcedony, or quartz). In some instances, the original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material.

The petrifaction process occurs underground, when wood becomes buried in water or volcanic ash. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. 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. During replacement, the plant's cell walls act as a template for mineralization. There needs to be a balance between the decay of cellulose and lignin and mineral templating for cellular detail to be preserved with fidelity. Most of the organic matter often decomposes; however, some of the lignin may remain. Silica in the form of opal-A, can encrust and permeate wood relatively quickly in hot spring environments. 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. A forest where such material has petrified becomes known as a petrified forest.

Formation

thumb|upright|Microscopic view of petrified Callixylon wood

thumb|Petrified wood mineralized with [[carnotite from St. George, Utah]]

thumb|Petrified wood from the Shinarump Formation at the Nacimiento Mine, Cuba, New Mexico. The brown wood at right shows conventional silica mineralization. The black wood at left shows unusual mineralization with chalcocite and other sulfide minerals. The blue-green stains are from oxidation of the chalcocite to azurite and malachite.

Petrified wood forms when woody stems of plants are buried in wet sediments saturated with dissolved minerals. The lack of oxygen slows decay of the wood, allowing minerals to replace cell walls and to fill void spaces in the wood. The wood is then mineralized to transform it to stone. Non-mineralized wood has been recovered from Paleozoic formations, particularly Callixylon from Berea Sandstone, but this is very unusual. The petrified wood is later exposed by erosion of surrounding sediments. Non-mineralized fossil wood is rapidly destroyed when exposed by erosion, but petrified wood is quite durable. Over time, almost all the original organic material is lost; only around 10% remains in the petrified wood. While wood petrified in this setting is only a minor part of the geologic record,

Most of the color in petrified wood comes from trace metals. Of these, iron is the most important, and it can produce a range of hues depending on its oxidation state. Chromium produces bright green petrified wood. Variations in color likely reflect different episodes of mineralization. In some cases, variations may come from chromatographic separation of trace metals.

Wood can also be petrified by calcite, as occurs in concretions in coal beds. Wood petrified by calcite tends to retain more of its original organic material. Petrification begins with deposition of goethite in the cell walls, followed by deposition of calcite in the void spaces. Carbonized wood is resistant to silicification and is usually petrified by other minerals.

Simulated petrified wood

Scientists have attempted to duplicate the process of petrification of wood, both to better understand the natural petrification process Early attempts used sodium metasilicate as a source of silica, but tetraethyl orthosilicate has proven more promising. A number of Ancestral Puebloan structures near Petrified Forest National Park were constructed of petrified wood, including the Agate House Pueblo. Petrified wood is also used in New Age healing.

Occurrences

Petrified wood is found worldwide in sedimentary beds ranging in age from the Devonian (about 390 million years ago), when woody plants first appeared on dry land, to nearly the present. Petrified "forests" tend to be either entire ecosystems buried by volcanic eruptions, in which trunks often remain in their growth positions, or accumulations of drift wood in fluvial environments. Amethyst Ridge at Yellowstone National Park shows 27 successive forest ecosystems buried by eruptions, while Petrified Forest National Park is a particularly fine example of fluvial accumulations of driftwood.

Areas with a large number of petrified trees include:

Africa

thumb|Chunk of petrified wood near El Kurru (Northern Sudan)

thumb|Petrified log and [[Welwitschia at Namibia Petrified forest]]

Egypt – petrified forest in Cairo-Suez road, declared a national protectorate by the ministry of environment, also in the area of New Cairo at the Extension of Nasr City, El Qattamiyya, near El Maadi district, and Al Farafra oasis.
Madagascar – Northwest Coast
Namibia – petrified forest of Damaraland
Sudan – petrified forest north of El-Kurru

Asia

China – in the Junggar Basin of Xinjiang, northwest China, the government has issued a crackdown on collecting of this material.
India – protected geological sites known for petrified wood are the National Fossil Wood Park, Tiruvakkarai (20-million-year-old fossils), and the Akal Wood Fossil Park (180-million-year-old fossils). Petrified wood has also been discovered in Dholavira in Kutch, Gujarat, dating back to 187–176 million years.
Japan – there is a fossilized forest preserved at Sendai City Tomizawa Site Museum
Indonesia – petrified wood covers several areas in Banten and also in some part of Mount Halimun Salak National Park.
Israel – several examples of petrified wood occur in the HaMakhtesh HaGadol in the Negev desert.
Pakistan – Sindh – Dadu – Petrified Forest at Khirthar National Park
Saudi Arabia – petrified forest north of Riyadh
Thailand – Bantak Petrified Forest Park in Ban Tak District has the longest petrified log in the world, officially measuring 69.7 metres.

Oceania

Australia – has deposits of petrified and opalized wood. Chinchilla, Queensland is famous for its 'Chinchilla Red'.
New Zealand:
Curio Bay on The Catlins coast contains many petrified wood examples.
Fossil Forest, Takapuna, Auckland, New Zealand
Titahi Bay Beach, Porirua, New Zealand

Europe

Belgium – Geosite Goudberg near Hoegaarden.
Czech Republic, Nová Paka – The most famous locality on Permian–Carboniferous rocks in the Czech Republic.
France – petrified forest in the village of Champclauson
Georgia – Goderdzi Petrified Forest Natural Monument.
Germany – the museum of natural history in Chemnitz has a collection of petrified trees, from the in situ Chemnitz petrified forest, found in the town in 1737.
Greece – Petrified forest of Lesvos, at the western tip of the island of Lesbos, is possibly the largest of the petrified forests, covering an area of over and declared a National Monument in 1985. Large, upright trunks complete with root systems can be found, as well as trunks up to 22 m in length.
Italy:
, petrified forest near Avigliano Umbro, Umbria (Central Italy), age Piacenzian.
, petrified forest near Soddì (Province of Oristano, Sardinia), age Chattian–Aquitanian.
Norway – Fossilized tropical forest in Svalbard
Ukraine – petrified araucaria trunks near Druzhkivka
United Kingdom
Fossil Grove, Glasgow, Scotland
Fossil Forest, Dorset, England

North America

thumb|Petrified logs at Petrified Forest National Park, Arizona, United States

Canada – in the badlands of southern Alberta; petrified wood is the provincial stone of Alberta. Axel Heiberg Island in Nunavut has a large petrified forest. In and around the North Saskatchewan river, around the Edmonton area. Blanche Brook, in Stephenville, Newfoundland, has 305-million-year-old examples.
United States
Petrified Wood Park in Lemmon, South Dakota
Ginkgo/Wanapum State Park in Washington state
Petrified Forest National Park in Arizona
Petrified Forest in California
Mississippi Petrified Forest in Flora, Mississippi
Cherokee Ranch petrified forest
Florissant Fossil Beds National Monument near Florissant, Colorado
Yellowstone Petrified Forest and Gallatin Petrified Forest, Yellowstone National Park, Wyoming
The south unit of Theodore Roosevelt National Park outside Medora, North Dakota
Gilboa Fossil Forest in New York
Athens County, Caesar Creek, Hueston Woods, Ohio
Black Hills Petrified Forest in South Dakota
Escalante Petrified Forest State Park in Utah
Agate Desert in the Upper Rogue River Valley near Medford, Oregon
Fossil Forest in the Catskill region near Cairo, New York
Valley of Fire State Park in Nevada
Bisti Badlands in New Mexico
Prince William Forest Park in Virginia

South America

thumb|Petrified log in Paleorrota geopark, Brazil

thumb|Puyango petrified forest, Ecuador

Argentina – the Sarmiento Petrified Forest and Jaramillo Petrified Forest in Santa Cruz Province in the Argentine Patagonia have many trees that measure more than in diameter and long.
Brazil:
in the geopark of Paleorrota, there is a vast area with petrified trees.
In the Heritage forest
('Fossil Trees Natural Monument') in Tocantins: petrified forests of dicksoniaceae (specifically Psaronius and Tietea) and arthropitys
Petrified forests of dicksoniaceae (specifically Psaronius and Tietea singularis) and arthropitys can also be found in the state of São Paulo
near Rio Poti, Piauí, Permian (around 280–270 million years ago).
Ecuador – Puyango Petrified Forest – One of the largest collections of petrified wood in the world.

References

External links

The Petrified forest of Lesvos - Protected Natural Monument
The Town Museum of Nová Paka
The Mississippi Petrified Forest
Encyclopedia of recreation and leisure in America