sedimentary
Fossilized Brachiopod/Bivalve in Limestone
Brachiopoda or Bivalvia fossil in Calcite/Limestone (CaCO3)
Hardness: ~3 (if mostly calcite), Color: Tan, beige, or light gray, Luster: Dull to earthy, Crystal structure: Microcrystalline or fossiliferous, Cleavage: None visible in the bulk rock, Specific gravity: ~2.6-2.7
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Physical properties
Hardness: ~3 (if mostly calcite), Color: Tan, beige, or light gray, Luster: Dull to earthy, Crystal structure: Microcrystalline or fossiliferous, Cleavage: None visible in the bulk rock, Specific gravity: ~2.6-2.7
Formation & geological history
Formed in marine environments where shells of benthic organisms accumulated in lime mud, which later lithified into limestone. The age can range widely depending on the location, often Paleozoic to Mesozoic era.
Uses & applications
Educational purposes, small collector's item, and study of ancient marine life. Limestone itself is used in construction and cement.
Geological facts
The ribbed structure visible in the specimen is very characteristic of brachiopods, which were extremely abundant in Paleozoic seas but are much rarer today.
Field identification & locations
Identified by the distinct ribbed shell shape preserved in a relatively soft matrix. Commonly found in limestone outcroppings worldwide. A drop of dilute hydrochloric acid will cause it to fizz.
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