sedimentary
Fossiliferous Limestone with Rugose Coral
Calcite (CaCO3) matrix containing Rugosa (order of extinct solitary and colonial corals)
Hardness: 3 (Mohs scale); Color: Gray to tan matrix with lighter inclusions; Luster: Dull/Earthy; Structure: Clastic or organic sedimentary texture; Cleavage: Rhombohedral in calcite crystals, none in fossils.
- Hardness
- 3 (Mohs scale)
- Color
- Gray to tan matrix with lighter inclusions
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Gray to tan matrix with lighter inclusions; Luster: Dull/Earthy; Structure: Clastic or organic sedimentary texture; Cleavage: Rhombohedral in calcite crystals, none in fossils.
Formation & geological history
Formed in warm, shallow marine environments from the accumulation of calcium carbonate and organic remains. This specimen likely dates from the Paleozoic era (Ordovician to Permian periods, roughly 488 to 251 million years ago).
Uses & applications
Primary use is in construction (crushed stone, cement manufacturing) and agriculture (lime). Fossil-rich specimens are valued in the education, paleontological, and amateur collecting markets.
Geological facts
The circular inclusion visible in the upper portion is likely a cross-section of a 'Horn Coral' (Rugosa). These were solitary coral polyps that lived in their own calcium carbonate shells. They are index fossils used by geologists to date rock layers.
Field identification & locations
Identify by looking for biological structures like circles, radiates, or shell fragments in a gray/dull matrix. It will react and fizz (effervesce) when exposed to a drop of weak acid (like vinegar) due to the calcium carbonate content. Commonly found in exposed cratonic regions of North America and Europe.
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