What Is a Petrified Tree?

Required Ingredients

• Petrified wood is a piece of wood that has been partially turned to stone, technically known as quartz crystal. The process involves both chemical and physical changes, and is known as permineralization. While the exact process remains a mystery because scientists have been unable to duplicate it in a laboratory, the basics are known. Permineralization requires four key ingredients: wood, mud, water and time.

Mud's Role in the Process

• The first step of permineralization requires that a piece of wood be quickly covered by mud. The mud acts as a barrier, preventing the organic wood from decomposing as it reacts to oxygen. Frequently, petrified wood is covered by mud containing volcanic rock. This is important because the ash is high in mineral content, which will be important later in the process. Lahars, or volcanic mudflows, are the best producers of petrified forests for this reason.

Three Possible Outcomes

• At this point, there are three options for the wood. First, it may simply disintegrate and be lost forever. Second, it may be compressed by the pressure of the overlying sedimentary layers, forming coal. This is similar to the process whereby peat is transformed into oil. Third, it may become petrified or fossilized.

Water's Role in the Process

• Once buried, mineral-rich water begins to percolate down through the soil to the wood. This water permeates the porous tissue of the wood, filling the pores and fluid voids. Over time, the minerals in the water precipitate out and crystallize in these spaces. The original tissue, primarily lignin, remains; however, it is encapsulated within the crystalline quartz matrix. Again, this process takes a very long time, on the scale of millions of years. This produces petrified what is commonly called petrified wood.

Fossilization

• Fossilization represents an additional step. Here, the minerals actually replace the organic structure, or tissue. This is the same process that occurs in the fossilization of bones. In this case, no original wood remains preserved. Rather, the entire piece, including the tissue, is replaced, leaving a solid piece of stone.

About the Minerals

• The primary mineral involved in permineralization is silica, which volcanic ash is rich in. When crystallized, silica forms a clear or white crystal. However, there are many other minerals which may be present in the water that produce a wide range of colors in the petrified wood. For instance, copper, cobalt, and chromium produce a greenish-blue color, while carbon and manganese oxides produce a black colorization. If manganese is present, the quarts will take-on a pink tint. It is these colors that make petrified wood a prized resource for jewelry.