No rock and mineral collection should be without a piece of petrified wood. This fascinating mineral looks like wood but is actually stone.
'Petrifaction' is a geological process whereby the original organic matter is gradually replaced by natural minerals. The word comes from Greek meaning 'wood turned to stone'.
The transformation takes place over thousands to millions of years. It's sometimes believed the organic matter turns to stone but that's not correct.
As many ancient trees fell they were quickly covered by volcanic ash or sediment which starved them of oxygen. This prevented decay from immediately setting in.
Minerals from groundwater slowly seeped into voids and spaces. When the water dried up the minerals crystallised which created a cast. Although most of the original organic matter decomposed, cell walls often remained intact and surrounded newly formed crystals.