How does the wood petrify?
The wood must first be covered with such agents as volcanic ash, volcanic mud flows, sediments in lakes and swamps or material washed in by violent floods. By any means which would exclude oxygen (anaerobic, no air and no bacteria) and thus prevent decay. A several number of mineral substances (such as Calcite, Pyrite, Marcasite) can cause petrifaction. 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: it may be agate, jasper, chalcedony or opal. The wood molecules (lignum and cellulose) become inseparably bonded to the silica molecules and it changes almost of the wood’s characteristics. The characteristic that it does not necessarily change its cell structure! The varied colours of petrified wood are caused by the presence of other minerals that enter the wood in solution with the silica.
