Calling all Petrified wood experts

[Earendil]

Hello everyone,

 

Merry Christmas! I have a few hunks of petrified wood I want confirmed, all three were found in the Denver area. I'm expecting that they're just all different examples of agatized petrified wood, but I want to make sure. The first two have been in my backyard since we moved here, the third my uncle found in his yard and gave to us. My question is, if they're all agatized petrified wood, how come they all look so different? Thanks in advance for any help you can provide!

[Thomas.Dodson]

I don't see anything to suggest these aren't all petrified wood (definitely most are despite the small pictures).

 

Chert (the greater group of sedimentary rock composed of silicon dioxide including agate, chalcedony, flint, etc.) takes on different colors based on the impurities and trace elements present in the structure. For example, the presence of oxidized and reduced iron gives a red and green coloration respectively, white is an indication of carbonate impurities, and black usually indicates organic matter.

[Earendil]

1 hour ago, Thomas.Dodson said:

I don't see anything to suggest these aren't all petrified wood (definitely most are despite the small pictures).

 

Chert (the greater group of sedimentary rock composed of silicon dioxide including agate, chalcedony, flint, etc.) takes on different colors based on the impurities and trace elements present in the structure. For example, the presence of oxidized and reduced iron gives a red and green coloration respectively, white is an indication of carbonate impurities, and black usually indicates organic matter.

Right, but can anybody tell me if these in particular are agatized, opalized, etc?

[Thomas.Dodson]

9 minutes ago, yardrockpaleo said:

Right, but can anybody tell me if these in particular are agatized, opalized, etc?

They're silicified but I usually don't bother with the small differences of definitions for chert, chalcedony, and their varieties like agate and jasper. It's confusing and seems to vary. I tried to refresh myself on them to better answer your question but I couldn't find a consistent definition. Let's try and go through it.

 

Chert and Chalcedony have the same chemical composition (micro or cryptocrystalline SiO₂) but are often differentiated. We are going to gloss over this to try and get to your question without being too technical. Next, Chalcedony is often subdivided into Agate and Jasper (some put jasper in Chert because of the differences we glosses over but we'll skip this). Both are still SiO₂. It has to be just translucent or sometimes banded and translucent to be considered agate. If it is opaque it is considered jasper. Some also define these by color but translucence seems to be more used. Jasper and agate can occur together. It's hard to tell from your photos but I'd call most of them jasper by this definition.

 

TLDR, the subdivisions of micro and cryptocrystalline silica are confusing and are not well agreed upon but you probably have a combination of mostly jasper and some agate in this wood.

 

 

[FranzBernhard]

9 hours ago, Thomas.Dodson said:

combination of mostly jasper and some agate in this wood.

Yes, this is indeed not uncommon at all: Jasper is the stuff replacing the wood. Agate (banded) is the stuff that fills voids; if unbanded, you may call the filling stuff chalcedony.

 

There is a good and historic important non-fossil example in Sicily, the Jasp-Agates of Guiliana:

Jaspers and Agates of Guiliana, Sicily (pdf, about 10 MB, many nice pics, in German).

 

Franz Bernhard