sedimentary
Coquina or Fossiliferous Sandstone
Fossiliferous Calcarenite (CaCO3 with SiO2 inclusions)
Hardness: 3-4 (matrix) to 7 (quartz grains); Color: Tan, beige, grey; Luster: Dull/Earthy; Structure: Clastic with visible shell fragments and lithic inclusions; Specific Gravity: 2.3-2.6
- Hardness
- 3-4 (matrix) to 7 (quartz grains)
- Color
- Tan, beige, grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (matrix) to 7 (quartz grains); Color: Tan, beige, grey; Luster: Dull/Earthy; Structure: Clastic with visible shell fragments and lithic inclusions; Specific Gravity: 2.3-2.6
Formation & geological history
Formed in high-energy marine shoreline or beach environments where shell fragments and mineral sediment accumulate and are cemented together by calcium carbonate over thousands to millions of years.
Uses & applications
Used historically as a building material (notably in Florida/Spain), as road base, or as aggregate for landscaping and erosion control.
Geological facts
This specimen contains a notable dark lithic clast (possibly basalt or chert) embedded in a lighter matrix of crushed shells and sand. It is often porous and can be quite lightweight compared to igneous rocks.
Field identification & locations
Identify by looking for visible shell bits and a gritty texture. It will typically react (fizz) when exposed to a weak acid like vinegar due to the calcium carbonate content. Common in coastal regions.
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