sedimentary
Fossiliferous Limestone (Crinoidal Limestone)
Bioclastic grainstone (CaCO3)
Hardness: 3-4 on Mohs scale; Color: Dark grey to brown matrix with white/cream fossils; Luster: Dull to earthy; Structure: Clastic with biological inclusions; Cleavage: None (conchoidal or irregular fracture).
- Hardness
- 3-4 on Mohs scale
- Color
- Dark grey to brown matrix with white/cream fossils
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 on Mohs scale; Color: Dark grey to brown matrix with white/cream fossils; Luster: Dull to earthy; Structure: Clastic with biological inclusions; Cleavage: None (conchoidal or irregular fracture).
Formation & geological history
Formed in warm, shallow marine environments where skeletal debris (primarily crinoid stem fragments or 'sea lilies') accumulated on the sea floor and were lithified over millions of years, often during the Paleozoic era.
Uses & applications
Used as building stone, decorative masonry, aggregate in construction, and as educational or collector specimens for fossil enthusiasts.
Geological facts
The ring-shaped fossils are sections of crinoid stems, also known as 'St. Cuthbert's beads'. Crinoids are echinoderms related to starfish, and they have existed for about 480 million years.
Field identification & locations
Identify by looking for small, washer-like or donut-shaped white rings embedded in a darker matrix. Commonly found in areas with exposed Paleozoic or Mesozoic seabed strata, such as the Midwest USA or parts of the UK.
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