Petrified wood

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Image:Tree, Petrified Forest, Calistoga, California.jpg

Petrified wood is a type of fossil: it consists of fossil wood where all the organic materials have been replaced with minerals (most often a silicate, such as quartz), while retaining the original structure of the wood. The petrifaction process occurs underground, when wood becomes buried under sediment. Mineral-rich water flowing through the sediment deposits minerals in the plant's cells and as the plant's lignin and cellulose decay away, a stone cast forms in its place.

Minerals such as manganese, iron, and copper in the water/mud during the petrification process give petrified wood a variety of color ranges. Quartz crystals are colorless, but when iron is added to the process the crystals become stained with a yellow or red tint.

Following is a list of minerals and related color hues:

carbon - black
cobalt - green/blue
chromium - green/blue
copper - green/blue
iron oxides - red, brown, yellow
manganese - pink/orange
manganese oxides - black
silica - white, grey

Petrified wood can preserve the original structure of the wood in all its detail, down to the microsopic level. Structures such as tree rings and the various tissues are often observed features.

Petrified wood has a Mohs hardness level of 7, the same as quartz. Materials scientists have been able to make artificial petrified wood recently [1].

Petrified wood is also the state gem of Washington.

[edit] Locations

Argentina. Considered to be one of the world's best petrified reserves, the Petrified Forest National Monument in Santa Cruz, the Argentine Patagonia has many trees that measure more than 3 m (10 ft) in diameter and 30 m (100 ft) long. Compared to petrified trees in the United States that measure less than 1.8 m (6 ft) in diameter, the trees of the Central Steppes of Argentina are significantly larger.
Czech Republic, Nová Paka. The most famous locality on Permian-Carboniferous rocks in the Czech Republic.
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 150 km² 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.
United States. A famous petrified wood site is Petrified Forest National Park in the U.S. state of Arizona. Wood from the area (though not from the park) is a prized commercial item, particularly cut and polished samples.
Australia has vast deposits of petrified and opalised wood.