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When trees are buried by sediment and protected from decay, they may become infiltrated by silica-rich water. These silica solutions fill cell spaces, and the silica binds to the cell walls, preserving the wood. Some preserved wood tissues retain the original cell wall, which becomes “fossilized” or encased in minerals. In other cases, the
original plant material is replaced by minerals and the wood becomes “petrified” or turned to stone.

Silica (SiO2) molecular structure.PNG

What is Silica?

Silica is a natural compound made of two major elements: silicon (Si) and oxygen (O2). The other name of silica is silicon dioxide, which
is often seen in the form of quartz. Silica is a major component of sand but it is also found in plants, animals and small amounts can occur in ordinary water.

Why does petrified wood have colours?

Wood is often mineralised with silica (SiO2), which itself has colourless-to-white hues. The silica-rich groundwaters that infiltrate wood typically contain a variety of minerals, and those minerals can add different colours to petrified wood. In 2016 two geologists, George Mustoe and Marisa Acosta, conducted a study on fossil wood samples of many different colours. They proved that the colours of silicified wood mostly come from trace elements, especially Iron (Fe). Iron in different abundance and oxidation states produces different hues including red, purple, yellow, brown, black, grey, and even dark green, while chromium produces a bright green. Two main factors involved in the origin of petrified wood colour include: 1) The type and concentration of trace metals. 2) The physical and chemical properties that cause different hues and patterns (e.g. diffusion, oxidation/ reduction, and groundwater infiltration along fractures and spaces).



  • Boonchai, N. (2021). Wonders of the Petrified Wood Museum. In U. Chittamvanich, I.B. Huegele (Eds.) The story of petrified wood around the world, history, fun facts, world famous people and petrified wood, gallery of photomicrographs, Bangkok: Lifestyle and Travel Media Co., Ltd., 100 pp.

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