What is Petrification?
Before petrification can begin, there has to be plenty of wood near a water source, an event occurs, and the trees are
knocked over, usually into the water source. Most water source contains calcium carbonate, the chemical that forms
limestone. To ensure petrification the wood is saturated with water, and eventually, as the wood moves downstream, it
becomes bunched together and buried by mud, silt, and ash. The logs that have travelled downstream now need to
become buried by mud and sediment, as well as being covered with some of the ash from a volcanic eruption.
Petrification occurs by the replacement, recrystallization or permineralization of the original plant. (Permineralization
just means that mineral material fills in the voids of the fossil-to-be rather than replacing or recrystallizing the original
materials). In almost every case, ground water is the agent that causes petrification and calcium carbonate are the main
replacing minerals.
How long it takes for petrification to occur depends on factors such as pH and temperature, but all things being equal,
groundwater saturated with calcium carbonate (calcite) acts the fastest because calcite is more soluble than silica or
other petrifying minerals. So if we accept the fact that petrification occurs as a continuum (in other words, a gradual
process from partial to complete replacement/recrystallization/permineralization). Under ideal chemical conditions,
petrification is possible in a few hundred years or even less. The tree must be sealed from oxygen to prevent decay. If it
is not sealed, bacteria will usually decompose the wood.
Modelling Petrified Wood
Materials
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Small pieces of wood, such as 4 cm long sections of small dowels, or similarly sized fresh twigs
5-10 lbs of playground sand
Food colouring (at least two colours, represents calcium carbonate)
Plastic wrap
6 small clear plastic cups
6 rubber bands
1 stirring rod or 1 popsicle stick
Water (at room temperature)
Introduction
This experiment will model the process of petrification. While performing the experiment, try to think of the natural
processes that the experiment is modelling. Before performing the experiment, read the instructions and predict what
you think your results will be. Record your thoughts in the section marked "Prediction" on your worksheet.
Instructions
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If necessary, cut the wood into small enough pieces to fit into the small cups.
Fill one cup 1/4 full with sand.
Place one or two pieces of wood in the cup on top of the sand.
Pour sand over the wood until it is completely covered. Your cup will probably be about 1/2 full (maybe even
more).
In another cup, fill it 1/2 full with water. Choose a colour from the food colouring. Put 6 drops of food colouring
in the water and stir with the stirring rod. Add drops of food colouring until the desired shade is reached. 10
drops are recommended.
Slowly pour the coloured water into the cup with the sand and wood pieces. Pour just a little at a time, and
watch it seep to the bottom each time.
Continue to add coloured water until the sand is completely and evenly saturated and a little water covers the
sand. It is best to have only about 1/2 cm of water on the surface of the sand. You do not have to use all of the
coloured water. Only use what you need.
Be sure that the wood is still buried after you pour the water in the cup. If not, push the wood under the surface
of the sand with the stirring rod or a popsicle stick.
Cover the cup with plastic wrap and place a rubber band around the outside. The rubber band and plastic wrap
should fit tightly around the cup.
Repeat the above steps with a different colour of food colouring, in a different cup.
Lastly, repeat the above steps without using food colouring, in a different cup. This will be the control of the
experiment.
After 1 week, uncover the experiment and observe changes that have taken place in the various pieces of wood.
Modelling Petrified Wood - Activity Worksheet
Prediction
Before you begin, tell what you think will happen.
Investigation
1. What physical characteristics of the wood have changed? How did these changes occur?
2. What part of natural petrification does the food colouring represent in this experiment?
3. Why were the cups covered with plastic wrap and a rubber band?
4. How would real petrified wood be different from the petrified wood that you created in the experiment? Why?
5. Explain the importance of the presence of water for petrification to occur.