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concretions - hand/display specimen of a sandstone concretion from the Palm Spring Formation

$ 7.50

Concretions are a typical structural feature of some sedimentary rocks, particularly sandstones. Early in the burial history of a rock, before it becomes solidified, a cement will precipitate around a nucleus, often a fragment of calcium carbonate, filling the pore spaces as the sediment becomes consolidated into rock. The sediment 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.

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 specimen: If more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a blue or 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. When a pair is shown, you get both.

Shipping: These specimens ship in a  Priority Mail package for $10.31 or less, depending on your zip code.  We'll refund any shipping overpayment as soon as your order is packed.

Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.