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What On Earth Is A Concretion?

8/30/2022

22 Comments

 
CONCRETION
The word "concretion" is derived from the Latin words "con" – meaning "together" – and "cresco" – meaning "to grow."
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A rock that grows? Is there really such a thing?
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Yes there is such a thing.  A concretion is a compact mass of mineral matter, usually spherical or disk-shaped, embedded in a host rock of a different composition. This hard, round mass of sedimentary rock cement is carried into place by ground water.
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They usually form early in the burial history of sediment, before the rest of the sediment has hardened into solid rock. Concretions, the most varied-shaped rocks of the sedimentary world, occur when a considerable amount of cementing material collects locally around a nucleus, often organic, such as a leaf, tooth, piece of shell or fossil, dead and/or decade matter - like a crab or fish. Most concretions form around marine invertebrates...but are not limited to marine life.
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Concretions vary in size, shape, hardness, and color, from objects that require a magnifying lens to be clearly visible to huge bodies 10 feet in diameter and weighing several hundred pounds.
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Concretions are world wide and to the surprise of many, the rock is very common.  In the geologic state of Oregon, the largest concentration of concretions can be found along the Cape Arago Headland sandstone cliffs, especially at Yoakum Point, Sunset Bay, Norton Gulch, Shore Acres, Concretion Cove, Simpson Reef, Cape Arago, and the "giants" at Fossil Point.
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These "grown together" rocks have a variety of origins that require geologists to integrate information from a variety of disciplines, including biology, chemistry, soil science, meteorology and geology itself.
Concretions are commonly misunderstood geologic structures. Descriptions dating from the 18th century attest to the fact that concretions have long been regarded as geological curiosities.
It is also a misunderstanding that the round rocks form by rolling down the river or the ocean waves move the rocks in the surf, eroding the rock down to a round rock.  They formed round, and can be found in the cliffs round.
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Concretions are often mistaken for dinosaur fossil eggs, turtle eggs or shells, animal bones, human artifacts and even extraterrestrial debris.
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They are actually not fossils, artifacts, or even debris from space, but a very common geologic phenomenon in all types of sedimentary rock; which include sandstone, shale, siltstone, and limestone.
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The round light colored rock, (left), is slowly eroding out of the sandstone cliff at Shore Acres State Park.  This concretion recently revealed itself. Eventually it will erode completely out of the cliff...but when, only time will tell.
In the photo, (left), Gus is sitting amongst a large collection of concretions partially embedded in a sandstone cliff on the south wall of Simpson Beach at Shore Acres State Park.  It is hard to determine what decade matter started these concretions, but it could be as small as a grain of sand, or crab, fish, and possibly a shell.
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Buddy and Nicole, collected concretions with much excitement from a rocky beach unofficially named "Concretion Cove". Their great finds are used as artwork in their living room.
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Brian and Tyler-Marie collected a few treasures as well.  In "Concretion Cove", you can find concretions from the size of golf balls to the size of bowling balls.
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Gus stands next to one of my favorite concretions. In this photo, the size of the rock is apparently no larger than a softball...but scroll back up to the second photo. (It is the same rock, photographed artistically close, to appear much larger than it really is.)
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In the photo above, Gus is standing in front of an unusual group of oddly shaped concretions along the Yoakum Point Concretion Wall complex.
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Concretions throughout the Cape Arago Headland are comprised mostly of silica, embedded in sandstone. Silica gives them a strength so solid that attempting to break them open only results in a destroyed rock of rubble...that is if you can break them at all.
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The "Giants"

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The "Giant" Concretions are located just north of Fossil Point - along the Coos River near the Charleston area. This phenomenal collection of concretions consist of anywhere between 150 to 170 rocks.
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These giant concretions do not indicate that the nucleus that started the formation is of a large format. These rocks could have also formed around the same size leaf, tooth or crab as those of the baseballs and bowling balls. Their size though could indicate the conditions were perfect to form over a longer period of time...allowing them to gain "giant" status.
In the photo on the (right), a giant concretion is slowly eroding out from the softer bedrock which entombed it. Only the rock's top 1/4 is currently exposed. Once out, the rock will be one of the largest "giants" in the area. Just how long it will take to be completely freed will depend on mother nature.
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To visit the "giants" it is recommended to go at low tide. Though you can still get to them at a higher tide, most will be underwater. It is also recommended to wear a good pair of boots...the area is very gooey and slippery.
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Brian, Tyler-Marie, and I took one full day and visited the five concretion complexes within the Cape Arago Headland...from the smallest marbles at Sunset Bay, to the "giants" of Fossil Point, to visit such geologic marvels in such a close proximity is amazing. 
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I never get tired of visiting, exploring, investigating and collecting these unusual natural formations.   I would love to pry the giant concretions open and see what started the rocks process.  But, most likely, the object inside could be as small as a grain of sand, or a shell.  It is unlikely that something "big" is inside.
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Though the Cape Arago Headland has the largest concentration of concretions in the state of Oregon, there are other locations throughout Oregon that inhabit these phenomenal formations. From the Cape Arago Headland areas, they form in pockets in a south-southeast direction. Concretions reveal themselves along landslides, highway road cuts, logging roads, streams, rivers, and rock quarries.
Concretions can even be found in masses at the 2000 foot level, shown on the (right) at the Upper Coquille River Falls. Concretions can also be found throughout Cape Blanco, and the Loon Lake area, east of Reedsport.
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Oregon law prohibits removing concretions that are embedded in a host rock. It is illegal and can be punishable by law. If the concretions are not attached to its host rock, then collecting is permitted, as long as they are collected by hand, and no tool or machinery is used to collect them and get them back to your vehicle.
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I have a great collection of Concretions.  Here are some of my favorite concretions within my personal collection. The shape of concretion (below) is unofficially known as a "Tear-drop -or- Raindrop" This rock is approximately seven inches wide and about twelve inches tall, and VERY HEAVY! It's one of my favorites!
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The duel concretion (below) is sometimes called a "Faternity Doll". It is more commonly refered to as a "Peanut". Two concretions growing close together have merged into one.
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The concretion (below) is a great example of showing how concretions are not all traditionally round. The two inch round concretion in the center grew into a tree branch also forming into a concretion. This specimen was found within a landside near the Cape Arago Lighthouse. The branch concretion was broken in several spots. I collected as many pieces of the branch that I could find and carefully glued them back together.
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Once a concretion can be "successfully" broken open, it can reveal a unique treasure. The rock (below) was found at Sunset Bay. It was a solid round rock at the time it was found. The rock was brought home and placed in the yard. Eventually, time and weather cracked the rock into four pieces, revealing the nucleus that started the concretion process...a mussel shell.
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The concretions throughout the Cape Arago Headland will mostly consist of a shell nucleus. If you're wanting to find a rare treasure of the nucleus being a crab, you'll want to venture into the mountains above Powers, Oregon. Located around 2000 feet above sea level, found along logging road cuts oval shaped concretions, likely to house crabs, abound. The rock consistancy is a softer and easier to break open.
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This excellent example, on the (left), recently sold on Ebay for over $400 dollars. The owner stated it was collected in the mountains near Powers Oregon...about any hour south east of Cape Arago. (I did not buy it!)

22 Comments
kim s
3/13/2015 12:24:26 am

Love all the pics and information on these!

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Susan Smith
3/13/2015 07:59:11 am

Steven
In the desert of western Wyoming we find these. Great fun to find not only the round ones but the odd shaped are great too.

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Michael Curtis
1/16/2019 01:46:11 pm

I love looking for fossils in Wyoming and I had no idea about this. Where? What is in them?

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Brian Dear
8/1/2015 06:49:16 am

Wow, great photos and write-up, well done! Thanks for sending it to me.

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Helen G link
2/12/2016 06:57:45 am

I have a concretion the size of gumball from a 25 cent machine. I found it in the volcano ruins at Roads End, which is now part of Lincoln City. A group of women were hiking at a summer very-low-tide. Two of us found a round rock in the same area. Some time later I took the rock to a rock collectors display at the Chinook Winds casino to find out what it is. No one there knew. This was since the casino was built, which was probably 20 yrs ago.
I now live in Dubuque Iowa and this concretion is on a shelf of other rocks and shells. Things from the coast. I have a sister who lives in North Bend and sends some of your photos to my face book page. Thanks for the wonderful photos and the iinformation.

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Chandra O'Leary
5/30/2023 03:16:45 pm

Roads End is one of our favorite places to hunt for rocks!

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Joe Neill link
3/14/2016 10:56:08 pm

Hi Steve: I enjoyed your concretion spread. I have admired these for years. While leading a Camp Fire club I talked a radiologist into doing a Cat Scan of one so we could see what was inside. Then when we saw the snail I talked a friend with a concrete saw to cut it so we could bisect the snail. How cool is that?

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Sherwin G link
5/31/2016 05:52:30 pm

This is the best blog on concretions I have ever seen! What a great source of information. Less than six months ago I went to a rock shop in Victoria BC and asked what you call round rock coming out of another rock... usually sandstone. We have a lot of these here on Mayne Island. But I am looking forward to a trip to Oregon to see some those you posted on the blog. Great Job. We just did a family treasure hunt where more than half of the clues led to various concretions. Check out my blog.

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Tamla Haynes
11/12/2016 12:33:00 am

I would like to show you a round rock I have from arkansas maybe you could tell me more about it

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holly black link
2/15/2017 10:09:09 am

I photographed concretions north of the Coquille river in 1961.
I took the photos to OMSI and asked why the "rocks seemed to be having babies". they explained concretions to me.
I am sure the forms I saw are long gone in the wave action.
loved the Blog.

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David Scalone
1/19/2018 03:30:51 pm

I found these when I dug my foundation for my house, Gaston Oregon at 350 above sea level, They were not hard yet, about 1-2 ft across with layers of different color soil. Could not figure out what they were, Many smaller ones also. If you dig them up or take them from the spring , they dry out and fall apart. How old are these things.
D. Scalone

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Craig McLanachan
12/29/2018 03:20:55 pm

Hi, I live on the South Island of New Zealand, fairly close to the famous Moeraki Boulders. While they are spectacular and visited by huge numbers they are just the tip of what can be found along the coast here. Like you I have a very long fascination with the various forms and the stories behind their creation. I have many thousands of pics and should have a site for them I suppose. Thanks for your most interesting site.

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Dave Erwin
4/23/2019 05:20:36 pm

There are also concretions on Arroyo Seco Rd, Borrego Springs, CA

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Carole Campbell
10/17/2019 08:00:02 pm

You don't know how interesting this is to me! I have some irregular formed concretions from Table Rock Lake in MO. I found them close to shore. Some have cracked and fallen apart, being outside. I have seen oval rocks sticking out of roadside cuts in KY and even tried to get one out but no luck. Could these be the mussel or crab centers that are described?

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MckinneyVia link
3/14/2022 03:41:54 am

I very much appreciate it. Thank you for this excellent article. Keep posting!

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Melissa Kooyman
9/6/2022 02:12:19 pm

That crab that sold on ebay was cleaned up quite well. This is how I came to this site. In NW Oregon-Nehalem river area ,I find concretions with fossils in them. I'm using a diamond bit in a dremel to take the stone away but SLOWLY.When I am done I'd like to finish the cleanse with vinegar(?) acid(?)...this is what I was researching for.....Nice fossil crab in that concretion or as we call it-mud ball.

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pradeep link
1/30/2023 08:46:44 am

terrific article. I appreciated the structure and the various pcs of information Thanks for sharing

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coupon4hub link
1/31/2023 10:38:06 pm

Nice Post Very Informative Article Thanks for sharing

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Clint Kelly
3/7/2023 05:34:59 am

A few years ago I was helping a friend clean some property north of Spokane, Wa bordering on the Pend Oreille River (pronounced pond oray). We would walk along the river and pick up Concretions mixed in with the river rocks. They mostly looked like turtles or seals or bones. I’ve thought about painting some and using them as gifts.

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Paul Kwiatkowski
8/14/2023 08:53:37 pm

they are actually interstichin balls... biological remains of the titans and other monstrosities that were mud flash boiled when the earth was flooded

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