An Amateur Concretion Question...

[lissa318]

Am I correct in my understanding that concretions are just rocks that are composed of sediment similar to where they are extracted from or found? I guess I am having a difficult time grasping the difference of a concretion from "just a rock." A friend of mine and his wife are going to Nevada and he said if I told him what they looked like they would bring me a bunch back... I know they don't all contain fossils but I would like to have a decent chance of cracking open one that is. What exactly do you look for??? Sorry if this is a dumb question... lol

Edited April 8, 2013 by lissa318

[Missourian]

Concretions formed as the sediment grains were cemented around some nucleus, such as a fossil (but not always). They form by various means. In the case of some fossils in ironstone concretions, CO2 produced by initial decomposition combined with iron in the groundwater to form iron carbonate (i.e. siderite). In other cases, concretions form for no apparent reason. In some cases, I've seen them merged into beds.

The best way (for me) to visualize how concretions form in sediment is to compare them to that kitty litter that clumps up when.... well, you know. At this stage, the litter is still uncemented sediment that contains 'concretions'. Next, pour some watered-down glue into the litter to form 'rock'. Now if you break up this kitty litter concoction (if you are so inclined), the 'concretions' should break out away from 'matrix'. Hope this helps.

[CH4ShotCaller]

I usually have to chisel pieces of shale either from the shale layer or find them where stream, river or tides have exposed or freed them from the sediments. Color and location of the sediments and knowing what sites are productive certainly helps. I will stop and check sediment exposures for 'new' sites. It's obvious when a concretion is exposed, stands out like a sore thumb.

As Missourian stated, not all have fossils inside.... I know. After years of hauling, digging, splitting and grinding, I have a gravel drive full of 'duds'. LOL, ya don't want to know how many I destroyed that actually had a good one in them. Now, after some pointers from Micropterus and DLB, I can spy the good ones and take the appropriate measures to save time and the fossil. Here, shape, color and size does matter when a crab concretion is found. But, I still take all concretions, you never know what could be waiting! Hope this helps a wee bit.

[lissa318]

Concretions formed as the sediment grains were cemented around some nucleus, such as a fossil (but not always). They form by various means. In the case of some fossils in ironstone concretions, CO2 produced by initial decomposition combined with iron in the groundwater to form iron carbonate (i.e. siderite). In other cases, concretions form for no apparent reason. In some cases, I've seen them merged into beds.

The best way (for me) to visualize how concretions form in sediment is to compare them to that kitty litter that clumps up when.... well, you know. At this stage, the litter is still uncemented sediment that contains 'concretions'. Next, pour some watered-down glue into the litter to form 'rock'. Now if you break up this kitty litter concoction (if you are so inclined), the 'concretions' should break out away from 'matrix'. Hope this helps.

I usually have to chisel pieces of shale either from the shale layer or find them where stream, river or tides have exposed or freed them from the sediments. Color and location of the sediments and knowing what sites are productive certainly helps. I will stop and check sediment exposures for 'new' sites. It's obvious when a concretion is exposed, stands out like a sore thumb.

As Missourian stated, not all have fossils inside.... I know. After years of hauling, digging, splitting and grinding, I have a gravel drive full of 'duds'. LOL, ya don't want to know how many I destroyed that actually had a good one in them. Now, after some pointers from Micropterus and DLB, I can spy the good ones and take the appropriate measures to save time and the fossil. Here, shape, color and size does matter when a crab concretion is found. But, I still take all concretions, you never know what could be waiting! Hope this helps a wee bit.

Missourian, your example is to the point and very vivid... hahahaha! Hoping I don't crack a fresh coprolite accidentally... (oxymoron statement???) LOL Thanks for the explaination of how formed. I have something i think is one in my freezer right now but not sure... We shall see. Still an "A" for effort right?! lol CH4, thanks for the advice and from what I've seen on here the shapes are definitely not restricted to round... are they ever really smooth or more sand like in texture? How would you describe the looks of a concretion to someone that doesn't know? Or any pictures someone can share to show a good example? I see a lot cracked on her but always the goods on the inside showing... Hahaha

[CH4ShotCaller]

Here's some from last year. I'm looking for a few other shots, will post here on your thread.

[CH4ShotCaller]

Here's some not 'lemon' shaped. The one on the left has something inside, not yet prepped.

Edited April 3, 2013 by CH4ShotCaller

[lissa318]

Here's some from last year. I'm looking for a few other shots, will post here on your thread.

10-17-2012 006.JPG

That is great! And please do... This is exactly what I wanted to see. Thanks!!!

[CH4ShotCaller]

I'm looking for a shot from last year, has a concretion in situ...

[lissa318]

The big one on the left? See I have a lot to learn... Your second pic shows pieces I never would have thought concretions... But I guess you can tell more by where they are when you find them? You dug all of these out of embankments?

[CH4ShotCaller]

The big one on the left? See I have a lot to learn... Your second pic shows pieces I never would have thought concretions... But I guess you can tell more by where they are when you find them? You dug all of these out of embankments?

I searched, can't find the pic of the concretion in the shale wall, bummer. Next trip out, I'll take more before I pop 'em out. These, as most I obtain, are found by chisel 'n hammer. Looking for fractures in the cliff wall or make my own fractures. LOTS of hammer and chisel time to expose a concretion. I get lucky at times and find one or two in the bar ditch after freezing temps cause the moisture in the shale to expand (mechanical weathering) and fracture, fall. Those are the gravy pickings !

Edited April 3, 2013 by CH4ShotCaller

[lissa318]

I searched, can't find the pic of the concretion in the shale wall, bummer. Next trip out, I'll take more before I pop 'em out. These, as most I obtain, are found by chisel 'n hammer. Looking for fractures in the cliff wall or make my own fractures. LOTS of hammer and chisel time to expose a concretion. I get lucky at times and find one or two in the bar ditch after freezing temps cause the moisture in the shale to expand (mechanical weathering) and fracture, fall. Those are the gravy pickings !

I would love to see those pics and thanks so much for the feedback! Your pictures helped. I picked some small ones up the last time I got out and saw what I thought might be some larger concretions stuck in the outcrop. I'm thinking now they definitely were... They were in there pretty good. Will have tools next time. Going to share your pics with my friend and hope you don't mind? Hate to have them bring back a bucket full of Nada... Hopefully one of these days I'll get to travel and look in different areas myself! I would love that...

[Missourian]

In KC, we have many beds that contain concretions. They are made up of calcium phosphate, siderite, limestone, chert, or.... I think that's it. Only one bed (phosphatic concretions in the Muncie Creek Shale) consistently produces fossils. A couple other beds do have fossils on occasion, but there are either too many concretions with no fossils, or there aren't enough concretions present to amount to much.

[CH4ShotCaller]

Good luck and no problemo on the pic sharing, if it helps you, it's a winner in my book!

[Fossildude19]

Here is a pic of concretions in a shale wall.

Near Buffalo, NY.

These concretions sometimes contain enrolled Trilobites.

Sometimes, there is nothing at all inside them.

Regards,

Edited April 3, 2013 by Fossildude19

[CH4ShotCaller]

Here's some pics that DLB sent me, the big one is a concretion Micropterus101 left behind.

[lissa318]

In KC, we have many beds that contain concretions. They are made up of calcium phosphate, siderite, limestone, chert, or.... I think that's it. Only one bed (phosphatic concretions in the Muncie Creek Shale) consistently produces fossils. A couple other beds do have fossils on occasion, but there are either too many concretions with no fossils, or there aren't enough concretions present to amount to much.

Here is a pic of concretions in a shale wall.

Near Buffalo, NY.

IMG_0784.jpg

These concretions sometimes contain enrolled Trilobites.

Sometimes, there is nothing at all inside them.

Regards,

Here's some pics that DLB sent me, the big one is a concretion Micropterus101 left behind.

DLB.jpg

DLB1.jpgDLB2.jpgDLB3.jpg

Awww, good point Missourian... We have a lot of chert and iron concretions here I believe... Do those type of rocks ever produce fossil concretions? And CH4, Thanks alot and has that big one been cracked??? I highly doubt I'm considered a good enough friend to go through all that trouble for me... hahaha! Fossildude, your pic really does help show how obvious they are insitu as opposed to just recognizing one in hand... Thanks for that!

[lissa318]

Here's some not 'lemon' shaped. The one on the left has something inside, not yet prepped.

004.JPG

Ch4, I picked up a rock the last time I went out that looks similar to some of yours maybe? Do you think freeze thaw would work on one like this? Do you guys think concretion? Found at the bottom of that large outcrop I posted a pic of awhile ago...

[CH4ShotCaller]

Ch4, I picked up a rock the last time I went out that looks similar to some of yours maybe? Do you think freeze thaw would work on one like this? Do you guys think concretion? Found at the bottom of that large outcrop I posted a pic of awhile ago...IMG_20130403_092456.jpg

Looks like a concretion to me! Not really knowing the age and critters of the material you're searching, but that looks good. Post more pics of the search area too, and I got bored with freeze/thaw. I like instant gratification and use a chisel 'n hammer after orientation and split 'em. OR, you could save it for a later day and get yourself a compressor with some air pens, etc.

[CH4ShotCaller]

Here's a few I'm goona start prepping today. I'll not get any of them completed by night fall, but orientate and start looking for appendages is the plan. Notice the odd-shaped one on the right, could be a double!

[painshill]

I posted this info previously when the question of concretions vs nodules cropped up. The conventional geological distinction between a nodule and a concretion is that concretions are formed around a nucleus by precipitation of minerals, whereas a nodule is a replacement body.

Typically, concretions form in sedimentary rocks or deposits when a mineral ‘cement’ fills the porous gaps around the sediment grains and then hardens. This is what makes the concretion more resistant to erosion than the sediment that it forms in, such that it may weather out of its host rock as a discrete lump. They are normally formed early on in the history of a stratum, after sedimentation has occurred. The word itself comes from the Latin words “con” and “crescere”… meaning “growing together”.

Depending on prevailing conditions, concretions can be “pervasive” (simultaneous filling through the entire area where there is porosity and then gradual hardening of the entire mass) or “concentric” (successive deposition layers precipitating and hardening in a gradual manner). Frequently they are round or ovoid, but any shape is possible – even highly irregular shapes.

The nucleus is frequently organic… a leaf, a shell, a sponge or whatever… and so concretions can contain fossils. In England, concretions of siderite have been found with WWII military ordnance inside them… so it doesn’t necessarily take a huge amount of time for them to form. There was also an infamous metal “artefact” found in the States within what was believed to be an ancient concretion. After cleaning and a more thorough inspection, it turned out to be a modern spark-plug.

By contrast, a nodule is a secondary structure – typically a solid replacement body of chert or iron oxides formed during diagenesis
(relatively low temperature and pressure modification) of a sedimentary rock. Chert (in limestone) and flint (in chalk) nodules form by recrystallisation of amorphous silica from dead marine organisms such as sponges and diatoms. They can also contain fossilized organisms.

They can also form in volcanic flows (from cooling and recrystallisation) or in ash deposits. Diagenesis may well alter the original
mineralogy of a nodule and the rock that it forms in, but it’s a less severe modification than metamorphosis.

Nodules are frequently round or rounded and may also be hollow, like geodes or vugs and may also have a crystal lining. They also
frequently exhibit shrinkage patterns, as in septarian nodules.

The truth is that these terms are used interchangeably without proper geological distinction and the term “nodule”, in particular, is
widely used by non-geologists to describe anything rounded or knobbly in shape.

I collect concretions for their geological interest as well as splitting them open to look for fossils. Here's a couple of funky ones that are never going to suffer the hammer:

These are glacial mud concretions from the last ice age... both from Washington State.

[DLB]

As for the large concreation I have not got it open it will take some time I'm trying to figure out how to attack that one at the moment

[DLB]

Ch4, I picked up a rock the last time I went out that looks similar to some of yours maybe? Do you think freeze thaw would work on one like this? Do you guys think concretion? Found at the bottom of that large outcrop I posted a pic of awhile ago... IMG_20130403_092456.jpg

To answer your ? Yes it looks as if it is a sand stone or heavy grain mud stone it might contain some thing but the only way to find out is to break it or work it out if u are in shur of a new area when finding con"s I alway break and ask ?'s later once u find a productive area take your time working them out.

[CH4ShotCaller]

I posted this info previously when the question of concretions vs nodules cropped up. The conventional geological distinction between a nodule and a concretion is that concretions are formed around a nucleus by precipitation of minerals, whereas a nodule is a replacement body.

Typically, concretions form in sedimentary rocks or deposits when a mineral ‘cement’ fills the porous gaps around the sediment grains and then hardens. This is what makes the concretion more resistant to erosion than the sediment that it forms in, such that it may weather out of its host rock as a discrete lump. They are normally formed early on in the history of a stratum, after sedimentation has occurred. The word itself comes from the Latin words “con” and “crescere”… meaning “growing together”.

Depending on prevailing conditions, concretions can be “pervasive” (simultaneous filling through the entire area where there is porosity and then gradual hardening of the entire mass) or “concentric” (successive deposition layers precipitating and hardening in a gradual manner). Frequently they are round or ovoid, but any shape is possible – even highly irregular shapes.

The nucleus is frequently organic… a leaf, a shell, a sponge or whatever… and so concretions can contain fossils. In England, concretions of siderite have been found with WWII military ordnance inside them… so it doesn’t necessarily take a huge amount of time for them to form. There was also an infamous metal “artefact” found in the States within what was believed to be an ancient concretion. After cleaning and a more thorough inspection, it turned out to be a modern spark-plug.

By contrast, a nodule is a secondary structure – typically a solid replacement body of chert or iron oxides formed during diagenesis

(relatively low temperature and pressure modification) of a sedimentary rock. Chert (in limestone) and flint (in chalk) nodules form by recrystallisation of amorphous silica from dead marine organisms such as sponges and diatoms. They can also contain fossilized organisms.

They can also form in volcanic flows (from cooling and recrystallisation) or in ash deposits. Diagenesis may well alter the original

mineralogy of a nodule and the rock that it forms in, but it’s a less severe modification than metamorphosis.

Nodules are frequently round or rounded and may also be hollow, like geodes or vugs and may also have a crystal lining. They also

frequently exhibit shrinkage patterns, as in septarian nodules.

The truth is that these terms are used interchangeably without proper geological distinction and the term “nodule”, in particular, is

widely used by non-geologists to describe anything rounded or knobbly in shape.

I collect concretions for their geological interest as well as splitting them open to look for fossils. Here's a couple of funky ones that are never going to suffer the hammer:

Dsc_0253.jpg

Dsc_0252.jpg

These are glacial mud concretions from the last ice age... both from Washington State.

Found some of those near Fox Island... the local name for those types are "Mud Babies".

[lissa318]

Here's a few I'm goona start prepping today. I'll not get any of them completed by night fall, but orientate and start looking for appendages is the plan. Notice the odd-shaped one on the right, could be a double!

003.JPG

I posted this info previously when the question of concretions vs nodules cropped up. The conventional geological distinction between a nodule and a concretion is that concretions are formed around a nucleus by precipitation of minerals, whereas a nodule is a replacement body.

Typically, concretions form in sedimentary rocks or deposits when a mineral cement fills the porous gaps around the sediment grains and then hardens. This is what makes the concretion more resistant to erosion than the sediment that it forms in, such that it may weather out of its host rock as a discrete lump. They are normally formed early on in the history of a stratum, after sedimentation has occurred. The word itself comes from the Latin words con and crescere meaning growing together.

Depending on prevailing conditions, concretions can be pervasive (simultaneous filling through the entire area where there is porosity and then gradual hardening of the entire mass) or concentric (successive deposition layers precipitating and hardening in a gradual manner). Frequently they are round or ovoid, but any shape is possible even highly irregular shapes.

The nucleus is frequently organic a leaf, a shell, a sponge or whatever and so concretions can contain fossils. In England, concretions of siderite have been found with WWII military ordnance inside them so it doesnt necessarily take a huge amount of time for them to form. There was also an infamous metal artefact found in the States within what was believed to be an ancient concretion. After cleaning and a more thorough inspection, it turned out to be a modern spark-plug.

By contrast, a nodule is a secondary structure typically a solid replacement body of chert or iron oxides formed during diagenesis

(relatively low temperature and pressure modification) of a sedimentary rock. Chert (in limestone) and flint (in chalk) nodules form by recrystallisation of amorphous silica from dead marine organisms such as sponges and diatoms. They can also contain fossilized organisms.

They can also form in volcanic flows (from cooling and recrystallisation) or in ash deposits. Diagenesis may well alter the original

mineralogy of a nodule and the rock that it forms in, but its a less severe modification than metamorphosis.

Nodules are frequently round or rounded and may also be hollow, like geodes or vugs and may also have a crystal lining. They also

frequently exhibit shrinkage patterns, as in septarian nodules.

The truth is that these terms are used interchangeably without proper geological distinction and the term nodule, in particular, is

widely used by non-geologists to describe anything rounded or knobbly in shape.

I collect concretions for their geological interest as well as splitting them open to look for fossils. Here's a couple of funky ones that are never going to suffer the hammer:

Dsc_0253.jpg

Dsc_0252.jpg

These are glacial mud concretions from the last ice age... both from Washington State.

Wow Painshill! That was wonderfully informative! Thank you. I certainly know more now than i did prior to reading that... And I for one would never be able to consider cracking those two either... They are fabulous just in themselves! CH4, oh I do really hope that is your double!!!!! lol! Let me know what you find in them, and you mentioned appendages on the plane... I'd that how you figure out where to split them? I'd like to know more about that. Here is where I found that concretion

Also picked up these two at the time thinking they might be...

In addition found a little one that the outer layer appeared to crack off naturally on the one side. Wondering if there is in fact something in there but can't see it? Maybe nothing but here is a pic of it, although not a good one.

[lissa318]

I also meant to add that this particular cut is in the Dunkard group which is considered Permian but I hear it is Pennsylvanian also... Different things are found in my county as opposed to areas of the Dunkard in West Virginia.