sedimentary
Fossiliferous Limestone (Crinoid stem)
CaCO3 (Calcium Carbonate) with Fossil Inclusions
Hardness: 3 (Mohs scale), Color: light grey to cream, Luster: dull to earthy, Crystal structure: rhombohedral (microcrystalline calcite), Cleavage: perfect rhombohedral in calcite matrix, Specific gravity: 2.71
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Physical properties
Hardness: 3 (Mohs scale), Color: light grey to cream, Luster: dull to earthy, Crystal structure: rhombohedral (microcrystalline calcite), Cleavage: perfect rhombohedral in calcite matrix, Specific gravity: 2.71
Formation & geological history
Formed in marine environments from the accumulation of organic debris such as shell, coral, algal, and fecal debris. These fossils often date from the Paleozoic era (approx. 250-500 million years ago).
Uses & applications
Used in the production of cement, as a building stone (dimension stone), in road construction, and the fossil specimens are popular for educational purposes and amateur collectors.
Geological facts
Crinoids are also known as 'sea lilies' and are related to starfish and sea urchins. The small cylindrical segments in the rock are parts of the stem that once anchored the animal to the sea floor.
Field identification & locations
Identify by a grey, fine-grained matrix that fizzes when exposed to warm diluted acid (HCl). Look for circular or disc-shaped impressions (crinoid columnals). Often found in limestone outcrops, quarries, and riverbeds across the Midwestern USA.
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