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 of the time that event is a volcanic eruption. 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 traveled downstream now need to become buried by mud and sediment, as well as being covered with some of the ash from the 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 silica and calcite are the main replacing minerals. 

In 1906 Professor Wieland created a theory on the petrification process of wood based on five variables:

1.The tissue systems of the plant

2. Temperature

3. Minerals necessary for the process of silification or calcification

4.Duration of chemical activity

5.The nature of the embedding rock material

The mineralization of the entire plant is first conditional on the tissue system, which is reliant on the state of growth, prefoliation, and preflorations of the plant species.Temperature, the surrounding sediments, and the abundance and type of minerals facilitate the petrification process. 

Altered Remains (changed structural and/or chemically)

• Permineralization - Mineral matter added to pores, cavities after burial. Makes preservation more likely by increasing durability.
• Recrystallization - Less stable crystal structures in shells, bones, etc. change to more stable structure after burial. No compositional change, just changes in crystal structure.
• Aragonite ---> calcite
• Opal ---> chert/silica
• Replacement - Original skeletal material is replaced by compound of a different composition.
• Apatite --> Opal
• Ca-Carbonate --> Pyrite/Silica
• Chitin --> Silica
• Wood --> Silica (Chert/Opal) or Calcite: "Petrified Wood"

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 replacment/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. 

To demonstrate the process of petrification using everyday objects. 

Materials

Activity Worksheet
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 coloring (at least two colors)
Plastic wrap
6 small clear plastic cups
6 rubber bands
1 stirring rod or 1 popcicle 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 modeling. 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

1. If necessary, cut the wood into small enough pieces to fit into the small cups. 
2. Fill one cup 1/4 full with sand. 
3. Place one or two pieces of wood in the cup on top of the sand. 
4. Pour sand over the wood until it is completely covered. Your cup will probably be about 1/2 full (maybe even more). 
5. In another cup, fill it 1/2 full with water. Choose a color from the food coloring. Put 6 drops of food coloring in the water and stir with the stirring rod. Add drops of food coloring until the desired shade is reached. 10 drops are recommended. 
6. Slowly pour the colored 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. 
7. Continue to add colored 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 colored water. Only use what you need. 
8. 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. 
9. 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. 
10. Repeat the above steps with a different color of food coloring, in a different cup. 
11. Lastly, repeat the above steps without using food coloring, in a different cup. This will be the control of the experiment. 
12. After 1 week, uncover the experiment and observe changes that have taken place in the various pieces of wood. 

• Students should understand the concept of having a control in a scientific experiment 
• Make sure the students have a firm understanding that the food coloring represents silica, or any of the other replacement minerals mentioned above. It can only be carried in water. 
• Try introducing new variables into the experiment and observe the changes, if any. Here are some examples of new variables for the experiment: 

- clay instead of sand
- temperature of water
- old chicken bone instead of wood
- salinity of water
- piece of plastic instead of wood

• Try using a different kind of sand or dirt. What does this tell us about the best petrification environments? 

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 coloring 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.