Concretions

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color and hardness. Often are mistaken for bones, fossils, meteorites and other odd objects. They can be so small that it requires a magnifying glass to be visible or as large as 10 feet in diameter and weigh hundreds of pounds. can also have somewhat of regular shapes such as boxes, blocks, flat disks, pipes, cannon balls and have even been known to resemble parts of a human body such as a foot or ribs.
are most commonly composed of calcite but sometimes can be composed of iron oxide or iron hydroxide such as goethite. But also can be composed of other minerals ranging from siderite, ankerite, dolomite, pyrite, baryite and gypsum.

Concretions form in many different ways. The box shape of some ironstone concretions most often depend on the way a sandstone or shale bed breaks up due to the action of weathering into regular blocks of various sizes. The way in which this separation takes place along natural planes of weakness in a rock such as a horizontal bedding ...

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by building up layers of material such as a nucleus as I stated before. The ground water around them contained with dissolved iron, calcium, silicon and other chemicals will drop them as calcium carbonate, silica solids or as iron oxide when the chemical conditions change. Every time this happens it forms a thin layer and as the layers build up they may contain different concentrations of compounds which in turn shows up as different colors.

Some concretions can also be hollow containing an empty center filled with powdery clay and sand or can include a detached hard lump resembling a nut. The loose powder in the middle can be explaind by the iron oxide has bee drawn away from ...

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