The Birth-Pangs of Petrified Wood
(silicified wood)
 

BACKGROUND:

The area of northeastern Arizona is now located at approximately 35 degrees north latitude in a temperate zone with four distinct seasons.  Around 200 million years ago thanks to tectonic shift, this same location was located in the equatorial tropics.  This was a verdant, warm, damp region with rivers and streams, not the arid and cold desert it is today.  Millions of conifers dotted the landscape, many topping 200 feet, accompanied by thousands of other temperate and subtropical species.  This setting provided food and shelter for a wide variety of primordial creatures.  Fossil deposits of this area are in the sediments of the Chinle Formation of the Colorado Plateau.  The entire landmass was on the western shores of Pangaea, the supercontinental 'mother' to our present continents.  It is this area that gave rise to the Petrified Forest areas of northeastern Arizona. 

Over eons of time normal weather patterns knocked over some of these conifers, depositing them under lowland flood plains or within streambeds, breaking them up along the way.  This process was accompanied by volcanic eruptions to the west which deposited millions of tons of mineral-rich volcanic ash onto the sediment and over the felled trees.  The vast majority of these trees simply decomposed, leaving no evidence of their towering existence at all.  A fortunate few, microscopic in comparison to the former forests remained, transformed into a beautiful permanence.  The fossilised remnants we see today are comprised of three now-extinct species: Araucarioxylon arizonicum, Woodworthia and Schilderia.  Their nearest relatives in the present world are the

Norfolk Island Pine      Norfolk Island Pine, Needle Structure

Araucaria Heterophyllia - "Norfolk Island Pine"

 Origin: Norfolk Island between Australia and New Zealand; Range: Widespread across the temperate climatic zones

Credit:  Purdue University Gardening Website

 

Monkey Puzzle Tree1     Monkey Puzzle Tree2

Monkey Puzzle Tree3 needle structure 

Araucaria Araucana - "Monkey Puzzle Tree"

Origin:  Chile and Western Argentina.  Range:  Widespread across the temperate climatic zones.

N.B.:  This tree is the "National Tree" of Chile 

Credit:  Purdue University Agricultural and Gardening Website

 

FROM BIOLOGICAL TO MINEROLOGICAL BEAUTY - PETRIFICATION:

The logs buried under sedimentary deposits before they could decompose were the fortunate few.  Ground water within the sediment dissolved silica from the volcanic ash and passed it through the tree remnants (logs, branches, roots).  Over hundreds of centuries, this mineral solution gradually crystallized as quartz, replacing the cell walls in the tree remnants completely.  What we see in these 'petrified wood' is in fact silicified wood - a mineral replacement so exact that it is a virtually "to-the-molecule" natural pseudomorph.  In some cases it is not only an exact mineral replication of the surface area and form, but also reveals much of the internal cell structure.  Various minerals have combined with the quartz to yield dazzling colour combinations (see Mineral Tincture section below).  While the exact process of cell structure replication is not yet known, the general molecular process of petrification can be described:  the configuration of silicon and oxygen permits an open bonding arrangement that enables other ions to occupy the interstitial positions in the molecules and bond to them, yielding these colours.     

Brazil, Petrified Palm     USA, Louisiana, Petrified Palm

Examples of preservation of external and internal form / structure

L: Petrified Palm, Maranhao State, Brazil - Credit: globalminers.com  R: Petrified Palm, Louisiana, USA - Credit:  petrifiedwoodmuseum.org

 

FROM THEN TILL NOW:

For well over 100 million years, burials of this nature and continental drift took place.  About 60 million years ago the entire area was uplifted, forming part of the Colorado Plateau.  Over time wind and water erosion removed layers of soil and rock, gradually exposing the Chinle Formation and it's petrified jewels.  Travellers to the Petrified Forest National Park can now see these brittle, fractured "tree remnant" Biographs scattered across the landscape by Mother Nature.  What an artist she is!

 

AROUND THE WORLD:

Northeastern Arizona is not the only location where petrified wood can be experienced.  Below are some photographs of petrified wood from around the globe:   

Australia, Queensland, Petrified Wood    

Queensland, Australia

 

USA, New Mexico, Bisti Wilderness, Petrified Wood 

Bisti Wilderness, New Mexico, U.S.A.

 

Brazil, Maranhao State, Petrified Wood 

Maranhao State, Brazil

 

USA, Utah, Escalante-Morrison Formation, Petrified Wood 

Escalante, Morrison Formation, Utah, U.S.A.

 

USA, California, Calistoga, Petrified Wood 

Calistoga, California, U.S.A.

 

Malagasy Republic, Madagascar Island, Petrified Wood

Madagascar Island (Malagasy Republic), S.E. Africa

 

India, Thiruvakkarai, Petrified Wood 

Thiruvakkarai, India

 

USA, North Dakota, Sentinel Buttes1     USA, North Dakota, Sentinel Buttes, Petrified Wood

Sentinel Buttes, North Dakota, U.S.A.

 

Thailand, Nakkon, Petrified Wood     Thailand, Nakkon, Petrified Wood1 

Nakkon, Thailand

 

China, Xinjiang, Junggar Basin, Petrified Wood1     China, Xinjiang, Junggar Basin, Petrified Wood2

China, Xinjiang, Junggar Basin, Petrified Wood3     China, Xinjiang, Junggar Basin, Petrified Wood4

Junggar Basin, Xinjiang Autonomous Region, People's Republic of China

 

MINERAL TINCTURE:

As indicated above, various minerals yield various colours.  Here is a description, colour by colour:

Red / Pink: 

The source of red and pink in petrified wood is hematite, a form of oxidized iron.  The depth and richness of the colour depends on the quantity of hematite.  As water carrying dissolved iron moves through the buried trees, it causes oxygen in the tree material to bond with the iron. 

Red Petrified Wood     Pink Petrified Wood

Credits:  L - bonanza.com  R - bearchele.com

 

Yellow / Brown / Orange: 

Goethite (FEO(OH))- a hydrated iron oxide - produces these colours. 

Yellow Petrified Wood     Orange Petrified Wood     Brown Petrified Wood

Credits:  L: therockshop.com     C: dreamstime.com     R: dreamstime.com

 

Green: 

Green colored petrified wood is via a minute amount of chromium (Cr) present, usually under 2-percent.  This colour is very rare. 

Green Petrified Wood1     Green Petrified Wood2

Credits:  L - fossilmall.com     R - fossilmuseum.net

White:

Pure silica (SiO2) produces white in petrified wood. 

White Petrified Wood1     White Petrified Wood2

Credits:  L - ioffer.com     R - lesminesdemaer.com

 

Black: 

Iron sulfide (FeS2) produces black petrified wood.   

Black Petrified Wood1    Black Petrified Wood2

Credits:  L - naturalstoneart.com     R - thegemshop.com

 

Blue and Purple: 

The presence of manganese dioxide (MnO2) results in a blue or purple colour to petrified wood. 

Blue Petrified Wood1     Blue Petrified Wood2

Credits:  L - ioffer.com     R - huntforgems.com

Purple Petrified Wood1     Purple Petrified Wood2

Credits: digforcrystals.com

 

Tan: 

This colour is produced by silica dioxide (SiO2) and is most often encountered in permineralised wood in which the cell structure is more accurately replecated.

Tan Petrified Wood1     Tan Petrified Wood2

Credits:  L - mineralgallery.co.za     R - moorelapidary.com