How do you identify concretions?

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A concretion consists of the same material as the rock around it, plus the cementing mineral, whereas a nodule (like flint nodules in limestone) is composed of different material. Concretions can be shaped like cylinders, sheets, nearly perfect spheres, and everything in between. Most are spherical.

Are concretions valuable?

Generally, calcareous concretions are valued much like pearls. Brighter colors and stronger saturations command higher prices. Rounds and ovals are more desirable, and other shapes are judged based on how symmetrical they appear. Smoother surfaces, higher luster, and larger sizes also increase value.

What is inside a concretion?

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 microcrystalline variety of quartz. The interior contains a lining of inwardly projecting crystals, usually quartz of many varieties.

Are concretions rocks?

Concretions are masses of mineral matter embedded within rock layers, including limestone, sandstone, and shale. They often take shape when minerals precipitating (settling) out of water collect around a nucleus, such as a pebble, leaf, shell, bone, or fossil.

Where can I find concretions?

Concretions are found near and far, from Western Kazakhstan to beaches in California. Usually the size of cannonballs, they form from water eroding a piece out of sedimentary rock. They almost look man-made. Many fossils of dead creatures have been found inside these strange deposits.”

How long do concretions take to form?

“However, our results show that concretions grow at a very fast rate over several months to several years.” This rapid sealing mechanism could explain why some concretions contain well-preserved fossils of soft tissues that are rarely fossilized under other conditions.

Why do concretions happen?

Concretions are mostly idiopathic and result from degenerative changes in the conjunctiva due to aging. Secondary causes include: An allergic or chronic infective disorder affecting the conjunctival surface such as trachoma, allergic keratoconjunctivitis, atopic keratoconjunctivitis.

What are concretion stones?

A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur.

What does a concretion rock look like?

What does a nodule rock look like?

Nodules commonly are elongate with a knobby irregular surface; they usually are oriented parallel to the bedding. Chert and flint often occur as dense and structureless nodules of nearly pure silica in limestone or chalk, where they seem to be replacements of the carbonate rock by silica.

What’s inside a geode?

The hollow interior often is nearly filled with inward-projecting crystals, new layers growing on top of old. The crystals are of quartz, less often of calcite or dolomite, and sometimes of aragonite, ankerite, hematite, magnetite, pyrite, chalcopyrite, and sphalerite.

What happens to rock fragments that get buried for a long time?

Usually, the rock pieces, called sediments, drop from the wind or water to make a layer. The layer can be buried under other layers of sediments. After a long time the sediments can be cemented together to make sedimentary rock. In this way, igneous rock can become sedimentary rock.

Where do concretions come from?

Several of the concretion photos that I have been sent are of rocks found by hunters, as are the two from South Carolina above. Hematite concretions and nodules are found anywhere that there are sedimentary rocks.

What is this small cylindrical concretion?

This small cylindrical concretion formed around the trace of a plant root in shale of Miocene age from Sonoma County, California. Gallery of Concretions. Photo courtesy Glen Carlson, all rights reserved

What are the different types of concretions?

Concretions can be shaped like cylinders, sheets, nearly perfect spheres, and everything in between. Most are spherical. In size, they can range from as small as gravel to as large as a truck. This gallery shows concretions that range in size from small to large.

What is the difference between a concretion and a nodule?