Pyritized Vs Geodized Vs Petrified And So On

[Wakaritai]

I've seen these terms around, but I've had a hard time finding consistent answers in google searches. Can someone explain these terms and related ones that I may not have come across yet?

I'm partly curious because I have some crystallized corals, but I don't know what to call them. Mostly clear crystals, but some blue and other colors.

And the other part is pure curiosity. I'm just like to understand more about the processes that alter and preserve fossils.

[tracer]

I've seen these terms around, but I've had a hard time finding consistent answers in google searches. Can someone explain these terms and related ones that I may not have come across yet?

I'm partly curious because I have some crystallized corals, but I don't know what to call them. Mostly clear crystals, but some blue and other colors.

And the other part is pure curiosity. I'm just like to understand more about the processes that alter and preserve fossils.

use google and the search engine here to research the terms. also look up pseudomorph. pyritized is replaced or covered with fes2 - iron sulfide. it's good because it's pretty, but it's bad because it's hugely unstable and converts to white powder. look up "pyrite rot". geodized would be a roundish hole (vug)in strata that gets filled in with layers of quartz that leaves a hole in the middle, usually with crystals growing on the inner surface. petrified is a misnomer for pseudomorphing, where there is greater or lesser replacement of an original organic piece of a critter or plant with mineral. the process is highly variable and hugely complex, so start with trying to understand diagenesis. mineral precipitation by bacteria in a reducing environment is one key concept that gets overlooked a lot.

nobody can even begin to adequately and accurately explain the terms you mentioned in a post here, or even thirty posts here. geology and paleontology are complicated.

[Shamalama]

When a plant or animal is buried it has a chance to fossilize. The fossilization process is complicated and differs based on the geological circumstances that the encasing rocks go through. For simplicity sake I'll use a clam shell as reference.

Fossil - When we talk about something being fossilized that means it has been buried by within sedimentary rocks like Limestone, Sandstone or Shale. The clam dies and is buried before animals or other processes destroy the shell. Over time the sediments surrounding the shell are compressed and become stone. During this time the original shell material can be replaced with another mineral or dissolved away to leave a mold.

Pyritized - The shell gets buried in a low oxygen, reducing environment then Pyrite has a chance to form. As the Pyrite forms on the shell it replaces the original shell material and thus the fossil is called "Pyritized". As the Pyrite breaks down it can become a white powder if unstable and thus destroy the fossil or it will oxidize and convert to the mineral Limonite.

Petrified - This term is usually reserved for wood fossils. After the wood is buried, groundwater percolates through the rock and replaces the organic cells of the wood with minerals. Sometimes this can result in a very detailed fossil that retains the original cellular structure of the wood. Other times you will get more of an Agate where the overall shape of the wood is preserved but not the individual cells.

Geodeized - The shell gets gets buried normally but is not filled with sediment and is hollow. As groundwater percolates through the rock, there is the chance it will deposit crystals within the hollow space of the shell. Thus you get a fossil that looks like a shell on the outside but inside has geode like crystals.

This is a quick, simplistic explanation off the top of my head. Tracer is correct in that you should look up the terms in more detail to better understand them.

[tracer]

the oversimplifications that occur in the minds of many regarding these processes in large part revolve around the concept that most of what happens is mechanical in nature rather than chemical. where you bog down in trying to actually understand what's going on is in the chemistry. if you progress to trying to grasp quantitative analysis, then just remember 2+2=5, for very large values of 2.

[Wakaritai]

That's exactly what I was looking for. I just didn't quite know where to begin. Now I have a basic understand that I can research further with the terms mentioned

Thanks!

PS: I think most of my understanding came from others that misunderstood the terms. I've been looking at sites with fossils and some seem to use some of the terms interchangeably.

Edited March 9, 2010 by Wakaritai

[pleecan]

Does this mean that if you suspect that your fossil is pyritized ... there is a very strong possibility that the fossil will disintegrate with time? Having said that does any one coat or protect their pyritized fossils? I currently have no protection on my pyritized fossils... I do no submerge them in oil to cut the oxygen off? I just store my pyritized fossil in a zip lock bag. My question to the forum... How do you protect your prized pyritized fossils?

Peter

Edited March 9, 2010 by pleecan

[tracer]

you have to be careful and read a number of the most detailed and "scholarly" sources you can find on the concepts, because there's way too much bad info. for instance, if you were to look up "how limestone forms", you might get a fairly simple explanation like, "well, a bunch of coral and sea shells collects on the ocean floor and gets compressed". that's not the kind of info you want. all limestone is not created equally. for instance, to understand "chalk" formation, you'd want to first know about atmospheric and marine environments of the cretaceous and read up on how the golgi apparatus in autotrophic eukaryote coccolithophorids generates the coccoliths that are the primary constituent of chalk and then where all and why that happens, and how the sedimentary coccoliths underwent compaction and cementation and then a substantive number of millions of years later ended up in your kid's hand drawing on a sidewalk.

coccoliths are cool.

[tracer]

Does this mean that if you suspect that your fossil is pyritized ... there is a very strong possibility that the fossil will disintegrate with time? Having said that does any one coat or protect their pyritized fossils? I currently have no protection on my pyritized fossils... I do no submerge them in oil to cut the oxygen off? I just store my pyritized fossil in a zip lock bag. My questtion to the forum... How do you protect your prized pyritized fossils?

Peter

google "pyrite rot" and "pyrite disease" and read about thirty of the hits and decide which method(s)of consolidation you feel are most likely to delay or prevent the issue for you. my personal solution has been to not collect specimens preserved in unstable minerals, but that concept is unacceptable to many.

[Wakaritai]

I wish I had plecan's problem... I've never found a pyritized fossil!

After reading tracer's first post I searched the forum using google ("site:www.thefossilforum.com blah blah") I came across another of the terms: agatized. After comparing what (little) I know about agates to the info here, I started to wonder. I assumed all of the these terms (with the exception of "fossil") were mutually exclusive. But could something be both, for instance, geodized and agatized? Or petrified and agatized? See the following post for what smilodon called agatized coral, that appears to meet the definition of geode as well.

http://www.thefossilforum.com/index.php?showtopic=9531&view=findpost&p=107878

I have a bunch of apparently geodized coral (light spherical corals that sound like they have loose crystals in them when I shake them). I'm debating on trying to dremel them open to see what's inside. I don't want to mess up the nicer coral ones... but for the ones that can hardly be recognized as corals anymore, I don't see what I have to lose. Although... I've tried cutting into a piece of solitary rugose coral before with abrasive wheel, only to get practically nowhere even after lots of noise and time. lol

The next time I'm at campus I'll search some scholarly journals on the subject. I should manage just fine with all these new terms to help

Edited March 9, 2010 by Wakaritai

[tracer]

well, there are numerous "common" terms for minerals, and for the various forms and colors they take, particularly quartz. soooo...google chert, chalcedony, jasper, agate, etc. ad nauseum and you'll start understanding that stuff. but yes, a geode can be considered agate, as the two terms describe different characteristics of the thing.

[Shamalama]

well, there are numerous "common" terms for minerals, and for the various forms and colors they take, particularly quartz. soooo...google chert, chalcedony, jasper, agate, etc. ad nauseum and you'll start understanding that stuff. but yes, a geode can be considered agate, as the two terms describe different characteristics of the thing.

Actually, I disputitate what Tracer pontificamated.

To me Agatized means the whole fossil has been replaced with Quartz on a microscopic level. This is a similar process to, but chemically different from those fossils in the Chalk formations that are replaced with Cryptocrystalline Quartz (var. Flint or Chert).

If there are hollow spaces with large Crystals inside the body of the former animal/plant then I would consider it to be Geodized as a Geode is hollow. You can, however, have a vug (small hollow space with crystals) within an agate.

[tracer]

not sure what you said, but the definitions of agate that i've looked up do not refer to fossils at all, or pseudomorphing. agate is quartz with a certain structure and visual appearance, which is frequently present in the walls of geodes. there is huge variety to the things considered "agates" since the common term is simply a human classification, and lots of the names of these sorts of minerals are subject to semi-spirited debate. my stuff is all jasper and agate and chalcedony - your stuff is all chert

[pleecan]

google "pyrite rot" and "pyrite disease" and read about thirty of the hits and decide which method(s)of consolidation you feel are most likely to delay or prevent the issue for you. my personal solution has been to not collect specimens preserved in unstable minerals, but that concept is unacceptable to many.

Thanks for the response Tracer! I am going to post this question in General discussion to get beter exposure... I am curious how our forum members deal with this....

PL

[Shamalama]

not sure what you said, but the definitions of agate that i've looked up do not refer to fossils at all, or pseudomorphing. agate is quartz with a certain structure and visual appearance, which is frequently present in the walls of geodes. there is huge variety to the things considered "agates" since the common term is simply a human classification, and lots of the names of these sorts of minerals are subject to semi-spirited debate. my stuff is all jasper and agate and chalcedony - your stuff is all chert

Ah, Pseudomorphing... that is what I left out of the Agatized process. True, Agates can be very variable and dependent on who's looking at them. I was merely referring to the idea of what I feel is an Agatized fossil vs. a geodized fossil. I have Jasper replaced, Agate replaced, Chert replaced, Calcite replaced, Pyrite replaced and plain old Quartz replaced fossils. Let's just agree to sort of agree in our own way.

Besides, you can have all that jasper, agate and chalcedony... my stuff is Opal!

[tracer]

Let's just agree to sort of agree in our own way.

Besides, you can have all that jasper, agate and chalcedony... my stuff is Opal!

oh, no, no, no, good sir! you're not getting off that easy

i've cut up a banded agate brazilian geode before to use the "side walls" with the banding for jewelry/cabs etc. even made a couple of rings out of it. my point is that the exterior shape and the interior cavity and crystals is what constitutes the construct of a "geode" to people using that common term. but that doesn't exclude the concept of the sides of the "geode" being made of "agate", as that common term is normally applied. i realize i've broadened the concepts from just that of agatized and geodized coral (heh), but still. to me, it's a classic logic gate - i can with a great degree of confidence say "shamalama is smart and a good guy", without having to fret over whether i should have said "or".

p.s. - your opal is a watery mineraloid gel slowly drying out and converting to chert, so don't get too attached to it.

p.p.s. - but you still rock, in a paleozoic way