Petrified Wood

Petrified
Wood

Nothing is more fun that to be walking across a field and
find a piece of petrified wood. Because it tells a story of a
beautiful tree that once existed perhaps millions of years ago.
and it has been preserved in its original shape and look for you to enjoy millions of years later.

But the question is: How does wood last so long? How can it
become so hard that it can last for millions of years? Well,
the answer is easier than you may think. Wood that has been preserved
is said to have been petrified. That being, that
there is actually no wood left in the piece. The wood died and
was gone many years ago. What you are actually seeing is where
minerals have replaced the wood, but in the same shape and form.
So that while you see the wood just as it looked millions of
years ago, it is actually a rock that has taken the form of the
wood. How does this happen? Let’s get in our time machine and
go back a few millions years ago……

We are going to go back in time 100 million years to a tropical
forest in what is now the State of Texas. Just about 30 miles
from my house. And while this part of Texas is now arid and many
miles away from the Gulf of Mexico, once upon a time it was a
lush green tropical paradise with huge conifer trees growing
all over the place. These tree are extinct today but they once
flourished throughout the area.

At some point in time the climate changed and the trees died.
They fell into a marshy swamp area and were quickly covered up.
The watery mud that covered them was rich in calcium, and eventually,
when the water dried up, the calcium filled in where the wood
once existed and those conifer trees became petrified wood, or
calcified wood, which ever you want to call it.

Let’s look at how the process worked…and at some examples….

We start out with a tree…like the one at left….living
happily on a much warmer tropical earth almost 100 million years
ago. As time goes by the tree gets old, or the weather changes,
and it dies and falls into the mud. Here is where our story picks
up…………

 

 

 

 

If you look at the specimen below you will see a very well
formed and well preserved conifer tree stump. It is dark because
it was exposed to sunlight for many years. But notice how well
you can see the growth rings still preserved. Although this stump
is pure calcite mineral now, it still has the same shape and
look of the tree stump when it died.

With appreciation to Rey and Carol Castro of San Antonio, Texas on whose property
this and many other specimens were found and donated to YourGemologist.com. It was my pleasure to work with Rey and Carol to dig a lot
of these specimens up on their ranch. We really appreciate their
help with YourGemologist.com.

Calcified conifer tree stump from Texas

Another view of the tree. Notice the 12 inch ruler on the floor.

One interesting point of this conifer tree is
that the inside has growth rings like a modern tree, but the
outside has a grainy texture like a palm tree. Below is a close
up of the outside layer of the tree stump…just like it looked
100 million years ago when it died.

Surface
of the tree stump

Cross section
of a piece of calcified wood Another
freshly uncovered calcified tree Below you see a cross section of a piece
of calcified, petrified wood. The white dots at the red arrows
are actually small glitters of shiny crystals that were difficult
to photograph. However, these are actually well formed calcite
crystals that are in the grain of the wood itself. Let’s go on
and look at some of these under the microscope….. Cross section
of calcified wood In the first microphotograph below you see the
red arrows pointing to the tiny but well formed calcite crystals
that make the piece of wood. Actually, the entire piece is pure
calcite where the calcite has replaced the wood material. The darkness you see in the photograph above is due to discoloration
due to sunlight. Below and up close you can still see the white
color of the calcite.

Below is another view of the same specimen shown
above. Here the red arrows point to very nicely formed calcite
crystals that have grown inside the wood grain. These specimens
are courtesy of Greg Albrecht and were found on his ranch
in south/central Texas. I appreciate his allowing us to learn
from these specimens. Well formed
calcite crystals And, of course, the most often seen petrified
wood has been replaced with silicon instead of calcite. Like
the Petrified National Forest in Arizona. Here the water was
full of silicon and it was silicon that replaced the wood and
is now what you see. As you can note from the specimen below,
you get a much more realistic look with silicon based petrified
wood because the calcite turns the wood white…the silicon keeps
natural looking colors. It is also this type of silicon created
petrified wood that forms many major opal deposits. Since opals
are silicon and water, that is the exact same ingredients that
make petrified wood. So most silicon based petrified wood is
really opals of various forms and qualities.

Chunk of silicon based petrified
wood

A nice piece of petrified tree
limb

More petrified wood showing the growth rings

Below is a nice look at a piece of petrified
palm tree. The important difference of this type of petrified
wood is that the wood itself is porous just like the original
formation. Compare this piece of petrified palm tree with the
other petrified wood on this page…

Below you will see some photographs from
the Petrified National Forest in the United States that I took
on a drive from Miami to San Francisco. You will notice that
these were originally very large trees when they were alive.
They lived in an area of a swamp, and when they died they fell
into the swamp and were quickly covered up. As a result they
were preserved until they silicon in the water could replace
the cellulose of the wood as it decayed. The result is that the
wood became petrified as you see below. And as erosion slowly
exposed the ancient petrified forest, it appears that tree were
uncovered as you can see below. Here are a few views of the
wonderful occurrence of petrified wood….. Please remember the
all of the trees you see below are almost 1 meter in diameter.

A petrified tree that has broken
into segments…

Large parts of petrified trees
litter the countryside…

A place where large trees once
lived. Each is about 1 meter in diameter

We hope you enjoyed our look at petrified wood. As you can see, there is a lot more to it than just a piece of wood.

At left you see a petrified log from the island nation of Madagascar. This log is almost 2 feet tall and weighs over 200 pounds.