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concretions - set of teaching hand/display specimens of sandstone concretions

$ 7.50

Concretions are a typical structural feature of some sedimentary rocks, particularly sandstones. Normally a fragment of calcium carbonate or other material in the sandstone will attract calcium carbonate that is dissolved in the groundwater as it percolates through the formation. The sand grains then become cemented into a rough sphere around that fragment. Occasionally neighboring concretions grow against each other and are cemented together.

These specimens subtly show differential weathering, where resistant layers stand out. These layers likely represent drier periods, where calcium carbonate cement accumulated more slowly.

Typically, concretions in this formation are round, though unusual shapes form a small percentage of those that have weathered out. Occasionally several concretions grow together as in several of these groups. They can range from the size of a pea to that of a beach ball. These have weathered out of the sandstone of the Plio-Pleistocene Palm Spring Formation.

Select a set: You can select a set by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil or one of those plus some number of coins, or you can let us make the selection.

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