sedimentary
Fossiliferous Limestone (Coquina / Shell Conglomerate)
Bioclastic Limestone (composed primarily of CaCO3)
Hardness: 3-4 on Mohs scale; Color: Gray matrix with white to tan shell fragments; Luster: Dull to earthy; Structure: Fragmental (bioclastic) matrix; Specific Gravity: 2.3–2.7
- Hardness
- 3-4 on Mohs scale
- Color
- Gray matrix with white to tan shell fragments
- Luster
- Dull to earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3-4 on Mohs scale; Color: Gray matrix with white to tan shell fragments; Luster: Dull to earthy; Structure: Fragmental (bioclastic) matrix; Specific Gravity: 2.3–2.7
Formation & geological history
Formed in high-energy marine environments (beaches or shallow reefs) where shells are broken by wave action and cemented over time by calcium carbonate. Most specimens date from the Paleozoic to Cenozoic eras.
Uses & applications
Used primarily as decorative garden stones, historical building material (especially in Florida and the Caribbean), and for educational/fossil collecting purposes.
Geological facts
Famous structures like the Castillo de San Marcos in St. Augustine, Florida, were built using coquina limestone because the 'spongy' nature of the rock absorbed cannonball impacts rather than shattering.
Field identification & locations
Identify in the field by looking for visible shell casts, molds, or whole fossils embedded in a fine-grained matrix. It will react (fizz) when exposed to a weak acid like vinegar due to the calcium carbonate content.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary