Petrified wood is a fossil in which the organic remains have been replaced by minerals in the slow process of being replaced with stone. This petrification process generally results in a Quartz Chalcedony mineralization.
It forms when plant material is buried by sediment and protected from decay due to oxygen and organisms. Then, groundwater rich in dissolved solids flows through the sediment, replacing the original plant material with silica, calcite, pyrite, or another inorganic material such as opal.
Radioisotopic dates zircons tell us that the trees in the Black Forest were deposited about 211 million years ago and those in the Blue, Jasper, Crystal, and Rainbow Forests were deposited around 218 million years ago.