Mazon Creek ID help

[CBOB]

Hey folks!

 

Just cracked open a nodule from Mazon River, Grundy County and wondering if its a fossil or just geologic?  I can't see any detail to determine that its a fossil.  It looks like could be a seed cone or coprolite but just guesses?  Any thoughts?  I found a lot of plant material there.

 

Thanks

 

[Fossildude19]

Coprolite, perhaps? 

 

@fossilized6s  @RCFossils

[Miocene_Mason]

Speaking from absolutely no experience, seed cone looks most similar to me.

[CBOB]

Thanks guys.  This one has me stumped.  

[KimTexan]

Looks like a concretion of some sort, maybe of a geode nature, but I'm no pro at this. You can read the geode section in the link and see if it rings true to your piece. 

 

https://www.priweb.org/outreach.php?page=Edu_Prog/earth101/concreations

We can see if someone else can confirm the concretion suggestion. 

[ynot]

1 hour ago, KimTexan said:

a concretion of some sort, maybe of a geode nature,

Sorry, but these two objects are not the same. A concretion can not be a geode and vice verse.

[CBOB]

Definitely not a geode but thanks for posting.  Its definitely a concretion.  I've been collecting Mazon Creek nodules for 5 or 6 years now and these can be tough fossils to ID.  I'm leaning toward just mineralization or a coprolite on this one.  But really that's just a guess.

 

 

[KimTexan]

On 10/17/2017 at 8:27 PM, ynot said:

Sorry, but these two objects are not the same. A concretion can not be a geode and vice verse.

Hum, I'm not sure what to say to your statement. I have a very different understanding of the origin of these bodies.

Many geodes originate from concretions or nodules. My understanding is that geode formation happens by 2 general means. I understand this is a significantly oversimplified, but here goes. Wikipedia is not all that authoritative in itelsf, but it is easily accessible from my phone. Anyway, from Wikipedia you can find these 2 means of geode formation:

• by the filling of vesicles (gas bubbles) in volcanic to sub-volcanic rocks by minerals deposited from hydrothermal fluids or
• by the dissolution of igneous nodules or concretions (that were deposited syngenetically within the rock formations in which they are found) and partial filling by the same or other minerals precipitated from diagenetic water, groundwater or hydrothermal fluids.

Also, within the link I posted from the Paleontological Research Institute's website they say "Geodes are spherical concretions with a hollow interior, ranging from 2 cm to 1 m in diameter. The outermost layer is generally composed of chalcedony, a brown waxy fibrous variety of quartz. The interior contains a lining of inwardly projecting crystals, usually quartz."

I think their definition is oversimplified and a bit narrow, but that's just my opinion. Not all concretions are geodes, but I believe it is a reasonable statement to say that some geodes have their origin in concretions.

 

I don't believe my statement was totally erroneous. I wasn't saying it was a geode. I believed it to be a form of concretion, but it could be a form of nodule too. My leaning towards something of a geode nature came from 4 observations:

1. There appears to have been some dissolution of minerals at one point, which reformed in the center. 

2. It appears to be sedimentary in nature and may have a component of chalcedony. It's hard to tell from the pic what rock/minerals are present.

3. It is nodular or concretion-like in nature.

4. It is generally round to oval in shape.

All of which are attributes of geodes, but not limited to geodes.

 

I'm no expert. I'm just a lover of science and nature. I know my understanding and education on the topic are limited. 

 

This link below gives a very thorough explanation of the formation of nodules and concretions.  It's a very good article that is well supported with primary research/reference articles. http://www.saltworkconsultants.com/blog/silica-mobility-and-replaced-evaporites-2-replaced-caso4-02

 

I don't believe he ever uses the term concretion though. As I understand it many people use the terms concretion and nodule interchangeably, but I believe a nodule is a replacement body, while concretions are formed by mineral dissolution and reformation.

 

 

[Miocene_Mason]

@KimTexan with my admittedly little knowledge I will say you are not typically going to find geodes in sedimentary rocks and if you do (and this is semantics which I'm not a fan of, always confusing me!) your probably looking at what's called a vug, or maybe some sort of karst feature if your in a area with a karstic topography. In the Mazon, cracks will fill with calcite. I wouldn't cal, this a vug though, not "crystally" enough. (Now on to @ynot educate me on anything wrong I've said, which I highly encourage)

[KimTexan]

1 hour ago, WhodamanHD said:

@KimTexan with my admittedly little knowledge I will say you are not typically going to find geodes in sedimentary rocks and if you do (and this is semantics which I'm not a fan of, always confusing me!) your probably looking at what's called a vug, or maybe some sort of karst feature if your in a area with a karstic topography. In the Mazon, cracks will fill with calcite. I wouldn't cal, this a vug though, not "crystally" enough. (Now on to @ynot educate me on anything wrong I've said, which I highly encourage)

 

OK, I may be digging myself in deeper here. I have no desire to step on anyone's toes. Hopefully providing a little information won't cause offense.

Here goes: Karst topography is most commonly found in carbonate sedimentary rock. Common examples are limestone and dolostone. I use to be really into spelunking. 

Geodes are themselves of sedimentary origin and the external structure is frequently composed of in large part sedimentary components. From what I've seen, calcedoney is common and it is a type sedimentary rock. Geodes can be found in lava and volcanic rock too, but most of what I've seen was found in sedimentary rock. Most (70% ish) of the land surfaces is made up of sedimentary rock. So odds are many, if not most, geodes are found in sedimentary rock. Limestone is the most common type of rock they're found in.

 

I did take a geology class close to 30 years ago. I can't say that I remember much, but I did learn a few rock types. I think I learned most of my geology from my dad though.

[KimTexan]

I found this on the Illinois state museum website. It uses the terms concretions and nodules interchangeably. 

[KimTexan]

@CBOB this is a link to Mazon creek database of fossils. Maybe you can find something similar on there.

http://www.museum.state.il.us/databases/geology/mazoncreek/graphical/index.html

[piranha]

30 minutes ago, KimTexan said:

@CBOB this is a link to Mazon creek database of fossils. Maybe you can find something similar on there.

http://www.museum.state.il.us/databases/geology/mazoncreek/graphical/index.html

 

 

Unfortunately this database has not been updated for quite a while.  Smithsonian has all the current Mazon Creek flora taxonomy:  LINK

[ynot]

4 hours ago, KimTexan said:

Geodes are themselves of sedimentary origin and the external structure is frequently composed of in large part sedimentary components.

There are some types of geodes that are sedimentary in origin. Mississippi valley type sedimentary geodes, geodized shells and corals are the most common.The parent sedimentary rock is usually not attached to the "geode" in this type.

Most geodes are volcanic in origin.

 

4 hours ago, KimTexan said:

calcedoney is common and it is a type sedimentary rock.

Chalcedony is a common type of agate that is white, but it is volcanic in origins, deposited by hot water solutions.

 

4 hours ago, KimTexan said:

Geodes can be found in lava and volcanic rock

That is where the majority of the geodes come from. Look at thundereggs, Brazilian amethyst geodes and mexican "coconut" geodes.

 

5 hours ago, KimTexan said:

Many geodes originate from concretions or nodules. 

A concretion is the lithification of existing strata by localized filling of the space between the particles the strata is made from, causing the strata to be cemented together. The lithification usually starts from a "seed" and grows outward causing a layered effect. Concretions are found exclusively in sedimentary rock, and some contain wonderful fossils. (Mason creek). If they are hollow it is cause by the dissolution of "softer" layers in the interior, and usually happens after exposure to weathering.

 

I nodule fills a void within a parent rock (gas bubbles in volcanic rock). It can have a hollow center and therefore be considered a geode but most are solid. This type of mineralization can also fill a hollow area of a shell, or the area left empty by the dissolution of a shell or other organic object. They form from the outer layers and grow inward.

 

I think there has been a tendency to describe some things with a more desirable name to try to make them more sellable.

There also seems to be a misguided tendency to use the terms "concretion" and "nodule" interchangeably when they really should not be.

 

This is My understanding of the difference between a concretion and a nodule or geode.

[westcoast]

I agree that the term concretion and nodule are often used interchangeably. Most often in a sedimentological context nodule is used as a general coverall term for any lumpy or bumpy shape found in a sediment and they are often then further described as concretions to indicate how they formed.

[KimTexan]

21 hours ago, ynot said:

There are some types of geodes that are sedimentary in origin. 

I think this may be in part a matter of semantics.

 

I'll start by saying I am not a geologist or paleontologist. My professional experience is in chemistry and clinical science. I have worked in research too. I'm a biologist as well and something of a naturalist or one who loves nature, the outdoors and natural wonders whether organic or inorganic. 

 

I am under the belief that the process by which geodes are formed is considered a sedimentary process. Whether the point of origin is in volcanic or sedimentary rock does not make them volcanic or sedimentary, that is merely their origin.

As I understand it, in simple terms, sedimentary rock is formed when mineral and/or organic materials are deposited and subsequently solidified as liquid is removed from them. Frequently that happens when the material is mixed or transported in or by a water based solution.

There may be other nuances as to how it is formed or transported, but deposition of mineral and organic materials and their subsequent solidification are the basic defining characteristics of the formation of sedimentary rocks.

Frequently sedimentary rock may create a whole layer or formation. The Bright Angel shale layer in the Grand Canyon being a good example. Other times sedimentary rocks may form as isolated deposits of various kinds. A few examples could be concretions, nodules and geodes or various mineral compounds. My limited understanding of geode formation is that they form via a sedimentary process. Granted some sedimentary processes also result in the formation of mineral deposits, but I'm not sure you can classify all mineral deposits as sedimentary. That's a whole other topic.  

 

Quote

Most geodes are volcanic in origin.

This may be another semantic thing. Geodes can be found most frequently in volcanic as well as limestone, a sedementary rock form. I have no knowledge as to which has a higher frequency though. I believe some of the more noted geode beds are in igneous rock formations.

Quote

Chalcedony is a common type of agate that is white, but it is volcanic in origins, deposited by hot water solutions.

Ahh, there is that word "deposition", which in my mind, implies sedimentary in nature. My understanding could be very limited and narrow though.

I believe agate is a type of chalcedony, not chalcedony a type of agate. Both are comprised of cryptocrystalline silica. The article I posted in a link above has an article called:

Silica mobility and replaced evaporites

is a very thorough, enlightening and eloquently written article about the formation and development of various forms of silica compounds including chalcedony and chalcedony in pseudomorph forms.

Chalcedony can be found in sedimentary, volcanic and metamorphic rocks. Again it arises in these rocks through what I consider to be a sedimentary process.

Quote

That is where the majority of the geodes come from. Look at thundereggs, Brazilian amethyst geodes and mexican "coconut" geodes.

I've seen some of these. I absolutely love the amethyst geodes. I'd love to find one one day. I've found amethyst is southwestern Arkansas, but that's as close as I've gotten.

Quote

A concretion is the lithification of existing strata by localized filling of the space between the particles the strata is made from, causing the strata to be cemented together.

That sounds a bit like a vug, but the vug remains attached or fused to the rock or material around it in the strata.

One of my questions has been can you really always know if it was a lithification vs a growing inward? It seems in some instances it is difficult to tell.

Quote

They form from the outer layers and grow inward.

That hat is a definition I had not heard of nodules. What if you have a concretion that developes a cavity, which then grows crystles inward? Surely such a thing exists. What is it called at that point?

 

Quote

I think there has been a tendency to describe some things with a more desirable name to try to make them more sellable.

There also seems to be a misguided tendency to use the terms "concretion" and "nodule" interchangeably when they really should not be.

I believe this is likely likely to be true, but even many geologists and Paleontologists seem to use them interchangeably.

Quote

This is My understanding of the difference between a concretion and a nodule or geode.

 

This example below is a diagram from the article "Silica mobility and replaced evaporites"

[doushantuo]

BTW: do not underestimate the complexities of the growth of concretions:often the only clues to formationare in e.g. distibution and abundance of various isotopes

 

 

 

 

 

 

 

 

[ynot]

On 10/20/2017 at 9:08 PM, KimTexan said:

I am under the belief that the process by which geodes are formed is considered a sedimentary process. Whether the point of origin is in volcanic or sedimentary rock does not make them volcanic or sedimentary, that is merely their origin.

As I understand it, in simple terms, sedimentary rock is formed when mineral and/or organic materials are deposited and subsequently solidified as liquid is removed from them. Frequently that happens when the material is mixed or transported in or by a water based solution.

I was at My club's annual show today, and I asked some people more knowledgeable about agates than Me.

The replies to some of Your questions / statements were...

 

Sedimentary rock is rock made from sediment, defined as particles of rock or organic material, transported and deposited by mechanical means. Wind, water or gravity.

 

Agate vs. chalcedony - synonyms and use is regional.

 

What type of rock is agate / chalcedony- sedimentary, igneous or metamorphic?

None of the above. It is considered an associated mineral because it forms in all three types of rock but is not an actual part of them. (surprised Me there.)

 

Although found in sedimentary and metamorphic rocks, agate / chalcedony  is most commonly associated with volcanic rock.

 

Agates are deposited from a solution where the individual atoms will bond when the pressure and temperature are correct and a catalyst causes the solution to become over saturated. This is not considered to be "sedimentation", but rather it is "precipitation from solution". It is also the way crystals form. 

 

A "vug" is a cavity filled with crystals within a mineral vein. A geode is a separate hollow shell with a crystalline lining of

the interior void.

 

On 10/20/2017 at 9:08 PM, KimTexan said:

That hat is a definition I had not heard of nodules. What if you have a concretion that developes a cavity, which then grows crystles inward? Surely such a thing exists. What is it called at that point?

Not a definition, but an explanation of how a nodule develops.

Nobody had heard of or seen a concretion that had developed into a geode. All said that the processes needed to make a geode from a concretion are complex and not likely to occur.

 

 

On 10/20/2017 at 9:08 PM, KimTexan said:

I believe this is likely likely to be true, but even many geologists and Paleontologists seem to use them interchangeably.

A concretion is a cementation of existing layers of rock where the concreting mineral fills the space between the particles in the layer of rock (sandstone, siltstone, limestone, chalk, etc.) that the concretion forms in. Chert and flint form in this manner (sometimes preserving fossils.), so are technically concretions but are often referred to as nodules. I have also heard many refer to iron concretions as nodules. (I think this is a shape thing).

But I have never heard an agate nodule referred to as a concretion, because it forms in a cavity within the bedrock (gas bubbles in lava, mold of organic material in sedimentary rock, etc.), not in the space between particles of the rock.

 

So "nodule" has a wider definition than "concretion". A concretion can be referred to as a nodule but a nodule is not necessarily a concretion.

 

I hope this will help to clarify the issue for You.

 

Regards,

Tony