Washington Symbols, Gemstone: Petrified Wood

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Petrified Wood

Adopted on March 12, 1975.

Petrified Wood is the US State Gemstone of Washington. Most of the petrified wood in Washington grew during the Miocene Epoch, some 5 -12 million years ago, when the state was swampy and mild, and played host to vast forests of cypress, oak, elm, and ginkgo trees.

The geological history of the state has encompassed many great changes, one of them being the many lava flows from volcanic fissures. Centuries ago, the interior of Washington was swampy and mild with many trees growing in wet areas. Layers of logs were preserved with each new lava flow, and as the layers grew deeper, many of the logs became waterlogged and lay protected in deep water - by any means which would exclude oxygen and thus prevent decay. A number of mineral substances (such as calcite, pyrite, marcasite) can cause petrification, but by far the most common is silica. Solutions of silica dissolved in ground water infiltrate the buried wood and through a complex chemical process are precipitated and left in the individual plant cells. Here the silica may take a variety of forms; it may be agate, jasper, chalcedony or opal. The beautiful and varied colors of petrified wood are caused by the presence of other minerals that enter the wood in solution with the silica. Iron oxides stain the wood orange, rust, red or yellow. Manganese oxides produce blues, blacks or purple.

Following is a list of minerals and related color hues:

Copper - green/blue
Cobalt - green/blue
Chromium - green/blue
Manganese - pink
Carbon - black
Iron Oxides - red, brown, yellow
Manganese Oxides - black
Silica - white, grey

The most famous petrified wood site in the state is Ginkgo Petrified Forest State Park near Vantage, and Saddle Mountain, and Yakima Canyon in Eastern Washington. Many types of wood are preserved at Ginkgo Petrified Forest State Park, but the abundance of ginkgo wood gave the park its name. Ginkgos are gymnosperm trees (non-flowering plants in the same grouping as pines, spruces, and cycads) that were thought to have gone extinct at the end of the Mesozoic Era until living specimens were discovered in China in the last century. Ginkgos are now widely cultivated in North America and the Far East, and are called "maidenhair trees" after the resemblance of their leaves to those of the maidenhair fern.

Despite its abundance, there are few published records of the history of petrified wood in the state. Two published reports of fossil wood from Western Washington did appeared in the Mineralogist (Anonymous, 1936) and Mineral News (Beck 1941). They both tell of a collection of fossil woods from the Chehalis Valley gathered by Hugh Brown and studied by the renowned pioneer of Washington's petrified wood, Professor George Beck, from Washington State College. Quoting Prof. Beck from the articles "...examples of red-to buff- colored silicified wood, mostly water worn pebbles... The absence of palm wood argues against earliest Tertiary for the Chehalis woods...These Chehalis woods match fairly well the lists from the old classic forests of Amethyst Mountain, Yellowstone..."

Is there a scientific name for petrified wood?

It depends on what form the petrification took. Silicified wood is the best known (popular), however, the petrifaction may be the result of other mineralisations such as calcite, dolomite, barite etc. The species names depend on the tree, or plant that has been petrified.

REVISED CODE OF WASHINGTON

RCW 1.20.090
State gem.
Petrified wood is hereby designated as the official gem of the state of Washington.

[1975 c 8 § 1.]