CONCRETION
The word "concretion" is derived from the Latin words "con" – meaning "together" – and "cresco" – meaning "to grow."
The word "concretion" is derived from the Latin words "con" – meaning "together" – and "cresco" – meaning "to grow."
A rock that grows? Is there really such a thing?
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.
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.
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.
 | 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. |
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. |  |
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.
  | 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. |
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.
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.
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.)
In the photo above, Gus is standing in front of an unusual group of oddly shaped concretions along the Yoakum Point Concretion Wall complex.
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"
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.
 | 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. |  |
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.
 | 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.
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. |  |
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.
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!
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.
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.
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.
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.
 | 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!) |
