limestone - tan silty limestone from the Carmel Fm. - teaching hand specimen

Description

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Tan silty limestone from the Jurassic Carmel Formation of Utah - teaching hand specimen
T
his 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 form of limestone composed entirely of the minute calcium carbonate shells of coccolthophores, 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.
These specimens fit in a 3.75" x 5" unit tray. In some cases, there will be one or two smooth saw-cut sides. Let us know if this is objectionable and we will ship an uncut specimen.
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