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Posted in response to agatized vs. opalized petrified wood from Nancy on December 21, 2001 at 20:11:00:

Re: agatized vs. opalized petrified wood

Nancy,

I found the following descriptions of Petrified Wood in my files but don't remember where it came from. I like to give credit when due but it seems the authors information was inadvertently left off. For this omission I apoligize to it's author. Perhaps this information will be helpful to you:

Petrified Wood Descriptions:

A fossil is defined as : The remains of a once living organism, generally one that lived prior to the last glacial period (e.g. 10,000 years before present). They include skeletons, tracks, impressions, trails, borings and casts. Fossils are usually found in hard rock, but not always (e.g. amber).
Allaby, M., editor, 1992, The Concise Oxford Dictionary of Botany; Oxford University Press.

Most fossil wood; petrified wood, metamorphic wood, opalized wood, agatized wood, jasper wood casts, agate wood casts and limb casts are the "cast" type of fossil as defined above. Carbonized wood is
usually like the impression type of fossil.

A cast is defined as : The secondary rock or mineral that fills a natural mold, producing a replica of a fossil.
Bates, R. L., Jackson, J. A., editors,(prepared by the American Geological Institute), 1976, Dictionary of Geological Terms, third edition; Anchor Books (Doubleday).

Fossil wood: is a general term which includes all of the other more specific types defined below.
Petrified wood: is a wood cast (broken or whole) that the secondary filling mineral quartz (silica) or another mineral saturated the wood and preserved its cell structure enough to differentiate (observe) individual cells of the woods structure.

Metamophic wood: is petrified wood (broken or whole) that originally had cell structure but lost it over time due to metamorphic or devitrification processes.

Opalized wood: is a wood cast (whole or broken) that the secondary filling mineral is the amorphous form of quartz, opal.

Agatized wood: is a wood cast (whole or broken) that the secondary filling mineral is the translucent form of cryptocrystaline quartz, agate.

A Jasper wood cast: is an unbroken wood cast that the secondary filling mineral is the opaque form of cryptocrystaline quartz, jasper.

An agate wood cast: is an unbroken wood cast that the secondary filling mineral is agate.

A limb cast: is generally an unbroken cast section of a limb, root or small diameter tree trunk.

Carbonized wood is usually compressed wood that has changed into some form of coal or a wood cast that carbonized before it incompletely mineralized but never compressed.

That is the simple part. Observation shows us that there are no definite lines of demarcation. Quartz may contain enough mineral inclusions to make it on the border between translucent and opaque, or it may contain portions that are opaque and portions that are translucent. A fossil wood specimen may contain portions that the secondary filling mineral is opal and portions where it is agate. Petrified wood specimens may have areas that have lost there cell structure preservation as well as areas that retained it.

I collect all types of Fossilized/Petrified Wood and enjoy all for their differences and beauty.

Joe D.

From Joe Dunleavy - December 23, 2001 at 10:11:40
Email: jpdunlea[ ]home.com

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