limestone - tan silty limestone from the Jurassic Carmel Fm. - hand/display specimen
This tan silty limestone is interbedded with shales in the Middle Jurassic Carmel Formation in southwestern Utah. Limestones are primarily biogenic in origin, being composed of the protective shells of small organisms that extract calcium carbonate from seawater to build their shells. There is a constant rain of microscopic shells and other calcareous parts onto the sea floor, which when accumulated and consolidated becomes limestone.
Chalk is a porous form of limestone composed entirely of minute calcium carbonate shells of coccolithophores, a unicellular phytoplankton. Coquina is a form composed of shells and shell fragments, only partly consolidated. When a limestone contains clay, it grades towards shale and is called an argillaceous limestone.
Because the composition of limestone is calcium carbonate, a limestone will strongly effervesce with dilute hydrochloric acid. Dolomite, which can have the same appearance as a limestone, is calcium-magnesium-carbonate, and effervesces only reluctantly. Often a dolomite will effervesce with acid only where powdered by a few taps of a geologist's hammer, a useful field test. This limestone is a good contrast with the more typical gray limestones. Students should understand that limestone is not always gray, and that it can vary in color.
In the field photo, Carmel Limestone forms the cliff, and limey shale forms the slope, typical landforms in arid areas.
Shipping: By Priority Mail. Click > here < for shipping rates. See comment at Note! Use back button to return to this page.
Select a specimen: You can select a specimen 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.
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.