Home » Gemstones » Opal » Opalized Wood


Opalized Wood


Author: , Ph.D., GIA Graduate Gemologist


Herringbone Sequoia

Herringbone Sequoia: These cabochons were cut from an opalized wood known as Herringbone Sequoia by Greta Schneider. The rough was found in the Snake River / Hell's Canyon area by an old-time rockhound in the mid-1900s and was sold as part of his estate. It is uncertain if it was found on the Idaho or Oregon side of the canyon. Whichever state it came from, it is a beautiful and unique material. It is definitely opalized wood (specific gravity = 2.106, spot refractive index = 1.48).

What Is Opalized Wood?

Opalized wood is a type of petrified wood that is composed of opal rather than chalcedony or another mineral material. It almost always consists of common opal, without play-of-color, but rare instances of petrified wood composed of precious opal are known.



Opalized Wood Cabochon

Opalized Wood: A cabochon made from opalized wood from eastern Oregon. This cabochon measures approximately 11.5 x 17 millimeters and weighs 5.35 carats.

How Does Opalized Wood Form?

One of the most common and best geologic environments for the formation of petrified wood is a forest buried by a volcanic ashfall. In this situation the ash buries the plants and protects them from decay and insect attack. The ash also serves as an abundant source of easily dissolved silica, which will be carried into the wood by moving groundwater where it precipitates in cavities and replaces the solid woody materials. Large deposits of petrified wood in Arizona, Oregon, Wyoming, Indonesia, Russia, Mexico, Brazil, and other parts of the world have formed in this environment.

In most situations, the petrified wood found in these deposits today is composed of chalcedony, but in some situations the wood is composed of opal. Both of these varieties of petrified wood often occur in a single deposit. Because they are both formed from dissolved silica, they are often called "silicified wood".



Opalized Wood Tumbled Stone

Opalized Wood Tumbled Stone: A large tumbled stone made from opalized wood. This stone is about 2 inches across.

How To Identify Opalized Wood

Silicified woods composed of opal can easily be distinguished from those composed of chalcedony by three physical properties. In many instances, the less-common opalized wood is not recognized because most people assume that it is chalcedony and testing is not done. Opal has a lower specific gravity, a lower hardness, and a lower refractive index. Any one of these can be used to separate opal from chalcedony.

 OpalChalcedony
Specific Gravity2.04 to 2.232.59 to 2.61
Mohs Hardness5.5 to 66.5 to 7
Spot Refractive Index1.39 to 1.481.53 to 1.54

Opalized wood can be just as beautiful as petrified wood composed of chalcedony. However, opalized wood has durability differences and is less suitable for some jewelry and lapidary projects. Opalized wood has a lower hardness and is more easily damaged by abrasion. It also has a lower tenacity and is more likely to break upon impact or exposure to stress.

Opalized Wood

Opalized Wood: A nice piece of opalized wood from Oregon. It is colorful, accepts a bright polish, and shows excellent wood grain. This specimen measures about 3 inches across.

Is Opalized Wood More Valuable?

Some people might hear the name "opalized" wood and assume that it is more valuable than other types of petrified wood. That would be definitely be true if the opal is "precious opal" and exhibits a fine play-of-color. Wood petrified by precious opal does exist, and fine specimens can sell for extremely high prices.

However, much opalized wood is common opal, and the seller often does not know that it is opal (rather than chalcedony) because testing was not done. An argument can be made that opalized wood should sell for a lower price because of its potential durability issues.



More Gemstones
  Diamond
  Common Opal
  Fire Agate
  100+ Gems
  Pictures of Opal
  Colored Diamonds
  Ruby and Sapphire
  Tumbled Stones

geology store

Find Other Topics on Geology.com:


Rocks
Rocks: Galleries of igneous, sedimentary and metamorphic rock photos with descriptions.
Minerals
Minerals: Information about ore minerals, gem materials and rock-forming minerals.
Volcanoes
Volcanoes: Articles about volcanoes, volcanic hazards and eruptions past and present.
Gemstones
Gemstones: Colorful images and articles about diamonds and colored stones.
General Geology
General Geology: Articles about geysers, maars, deltas, rifts, salt domes, water, and much more!
Geology Store
Geology Store: Hammers, field bags, hand lenses, maps, books, hardness picks, gold pans.
Earth Science Records
Earth Science Records: Highest mountain, deepest lake, biggest tsunami and more.
Diamond
Diamonds: Learn about the properties of diamond, its many uses, and diamond discoveries.