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Petrified wood (from the Greek root "petro" meaning "rock" or "stone", literally "wood turned into stone") 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 and is initially preserved due to a lack of oxygen. 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 mould forms in its place.
Elements such as manganese, iron and copper in the water/mud during the petrification process give petrified wood a variety of color ranges. Pure quartz crystals are colorless, but when contaminants are added to the process the crystals take on a yellow, red or other tint.
Following is a list of contaminating elements and related color hues:
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 of 7, the same as quartz.
Petrified wood is the provincial stone of Alberta and also the state gem of Washington.
Additional recommended knowledge
Artificial petrified wood
Artificial petrified wood has been produced in a Washington lab. In the process small cubes of pine were soaked in an acid bath for two days then in a silica solution for another two. The product was then cooked at 1400 °C in an argon atmosphere for two hours. The result was silicon carbide ceramic which preserved the intricate cell structure of the wood. Soaking in a tungsten solution produced a tungsten carbide petrified wood. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Petrified_wood". A list of authors is available in Wikipedia.|