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 mould forms in its place.
The wood is preserved due to a lack of oxygen.
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:
carbon
- black
cobalt - green/blue
chromium - green/blue
copper - green/blue
iron oxides - red, brown, yellow
manganese - pink/orange
manganese oxides - black
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 also
the state gem of Washington.
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