Petrified wood is a type of fossil: it consists of fossil wood where all the organic materials have been replaced with minerals 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.
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 State.
