top of page
Concretions typically form around a solid core called a "nucleus". This is often composed of organic material, such as a leaf, tooth, piece of shell or fossil. A mineral solution (that is, a mineral dissolved in water)then precipitates around the nucleus and cements a covering.
The mineral solution is usually part of the host rock. In sandstones it is commonly calcium carbonate. Some concretions have iron oxides as the cement for their cases.
bottom of page