Petrified wood, also known as Fossilized Wood, is fossilized remnants of ancient trees from the Paleocene Era. The name "Petrified" came from the Greek "petro" that means "stone" implying that "wood turns to stone". During the long-term process lasting millions of years, called petrification, the wood structure completely transformed into mineral (stone). The wide varieties of colors are the result of mineral impurities that were presented during the petrification.
Here are types of petrified wood:
- Opalized wood - the original structure was replaced by opal
- Agatized wood - the wood, cell by cell, has been replaced by chalcedony, jasper, or agate
- Silicified wood - the cellular structure of the wood has been replaced by any form of silica, including opal and agate.
Petrified wood formed from ancient walnut, Myrtlewood, sycamore, and birch. The petrification process involves the gradual cellular replacement of decayed organic material by quartz crystals such as agate, jasper, amethyst, opal, or citrine. Ancient trees were washed into rivers or lakes, buried in sediments with the presence of volcanic ash in the anaerobic (oxygen-free) environment. The groundwater dissolved silica from the ash. The porous wood structure absorbed the silica-rich water, and, over time, the wood tissue was dissolved and replaced with minerals. This type of fossilization preserves the wood remarkably well allowing us to easily recognize fine details including growth rings, veins, and bark.
If the wood structure is either decayed or burned out, fossilized wood can be formed as Limb Casts. The limb-shaped cavity is filled with chalcedony and other minerals from groundwater, completely occupying the space left behind. As a result, the interior of the limb cast does not preserve the fine details of this tree, but the outer surface may show bark or wood knots.
How to Identify Petrified Wood?
Larger pieces of petrified wood may be easily identified if the specimen has the original shape and structural details are very well preserved. Check:
- If you can see the circular structure of annual rings when looking at either end of the piece
- If the surface of the specimen resembles tree bark.
The identification of petrified wood can be a difficult task if the specimen is small or if its inner structure has been lost (limb casts). Some small pieces of petrified wood can look like agate but agate exhibits a more rounded shape.
Petrified Wood Color
The black color is an effect of carbon and manganese presence; green and blue - cobalt, chrome oxide, and copper; yellow, red, and brown - iron oxide; pink and orange - manganese; yellow - manganese oxide, white - silicates of aluminum.
Where to Find Petrified Wood?
Oregon is known for many places where you can find petrified wood and legally take it for your collections. A wide variety of fossilized wood can be found on gravel bars of the rivers, reservoir and lake shorelines, on ocean beaches, fields, quarries, and at designated public collecting sites.
Hampton Butte is well-known among rock collectors for its unique green petrified wood...
Where to Find Limb Casts?
Limb Casts are found in public rockhounding areas of Central Oregon near unincorporated communities of Crook County Post and Paulina.
How Many Petrified Wood I Can Collect?
The legality of collecting minerals is pretty complex. Each jurisdiction has its own regulations which you always need to verify and comply with.
The collection of petrified wood from some public land in the United States is allowed for personal use. It means that you are not planning to sell it. According to BLM regulations in Oregon and Washington, the amount is limited to 25 pounds each day, plus one piece, but no more than 250 pounds during any calendar year. Quotas between two or more people may not be pooled to obtain pieces larger than 250 pounds.
Check with BLM for the current regulations and specific locations.
The U.S. Forest Service limits amounts of specimens up to 10 pounds. Some lands within the National Forest are closed for collecting due to wilderness designation.
Contact the U.S. Forest Service for up-to-date information.
Read more about Rockhounding Regulations and Rules on public lands of the state of Oregon.
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