Detailed studies have demonstrated that concretions form after sediments are buried but before the sediment is … See more

Concretions vary in shape, hardness and size, ranging from objects that require a magnifying lens to be clearly visible to huge bodies three meters in diameter and weighing several thousand pounds. The giant, red c… See more

Concretions are commonly composed of a mineral present as a minor component of the host rock. For example, concretions in sandstones or shales are commonly formed of a carbonate mineral such as calcite; those in … See more

Concretions are found in a variety of rocks, but are particularly common in shales, siltstones, and sandstones. They often outwardly resemble fossils or rocks that look as if they do not belong to the stratum in which th… See more

Concretions vary considerably in their compositions, shapes, sizes and modes of origin.
Septarian concretions (or septarian nodules) are carbonate-rich concretions containing … See more

• Bowling Ball Beach – Beach in Mendocino County, California, US
• Caliche, also known as calcrete – Calcium carbonate based concretion of sediment in arid and semi-arid soils… See more