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Petrified Wood
Some ancient wood escaped the natural process of decay by being buried in sediments or volcanic ash.  In some cases, dissolved minerals seeped into cellular voids and crystallized.  The most common minerals were calcite or silica.  When the cells of the wood have been replaced by the latter, they are said to be silicified or converted into silica. The result is commonly called "petrified" or "agatized" wood.  The most important deposits are in the western part of the United States in Arizona, California, Oregon, Utah, Washington and Wyoming.  Specimens of silicified wood from the Eden Valley, Wyoming are perfect casts of the original twigs and limbs of more than fifteen different forests of sequoia, pine, chestnut and plant trees. 
A number of mineral substances such as calcite, pyrite, marcasite can cause petrification, but by far the most common is silica.  Solutions of silica dissolved in ground water infiltrate the buried wood and through a complex chemical process are precipitated and left in the individual plant cells.  Here the silica may take a variety of forms such as agate, jasper, chalcedony or opal. 
The beautiful and varied colors of petrified wood are caused by the presence of other minerals that enter the wood in solution with the silica.  Iron oxide stains the wood orange, rust, red or yellow; manganese oxide produces blues, blacks or purple; and pine quartz for white and gray.
The Petrified Forest National Park in Arizona has wonderful examples of petrified wood, from small pieces, to large petrified logs.  We have provided some images from this park for you to see and enjoy
Petrified wood, not unexpectedly, is much heavier than the original log.  It may weigh as much as 150-200 pounds per cubic foot.  Unfortunately, pilfering and removal of the specimens of petrified wood continue to this day.  Some 25,000 pounds of wood are removed from one park each year.  Fortunately, it is difficult to remove the larger pieces, such as the petrified logs shown.
To see examples of the petrified wood that we have found, simply click on the image below.
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