sedimentary
Fossiliferous Limestone (Crinoidal)
Crinoid Limestone (CaCO3 with fossil biological remains)
Hardness: 3 (Mohs scale); Color: light gray to bluish-gray; Luster: dull to earthy; Crystal structure: orthorhombic or hexagonal (calcite/aragonite); Features: visible fossilized segments known as columnals.
- Hardness
- 3 (Mohs scale)
- Color
- light gray to bluish-gray
- Luster
- dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: light gray to bluish-gray; Luster: dull to earthy; Crystal structure: orthorhombic or hexagonal (calcite/aragonite); Features: visible fossilized segments known as columnals.
Formation & geological history
Formed in shallow, clear marine environments from the accumulation of skeletal remains of crinoids (sea lilies) and calcium carbonate precipitation. Age typically ranges from the Paleozoic era to the present.
Uses & applications
Used primarily in construction (aggregate, cement), as architectural stone, for agricultural lime, and for educational fossil collections.
Geological facts
Crinoids are marine animals, often called 'sea lilies' because they resemble plants. The fossilized stem segments seen in this rock are frequently called 'St. Cuthbert's beads' or 'star-stones' in folklore.
Field identification & locations
Identify in the field by looking for small, round, or star-shaped indentations/segments on limestone beach pebbles. These are common in Paleozoic formations globally, such as the UK and Midwestern US.
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