sedimentary
Coquina (Fossiliferous Limestone)
Coquina (Organic Clastic Limestone)
Hardness: 3 (on Mohs scale); Color: Brown, gray, or tan with visible shell fragments; Luster: Dull or earthy; Crystal structure: Amorphous/clastic; Cleavage: None (friable/fragmentary); Specific Gravity: 2.3-2.5
- Hardness
- 3 (on Mohs scale)
- Color
- Brown, gray, or tan with visible shell fragments
- Luster
- Dull or earthy
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Physical properties
Hardness: 3 (on Mohs scale); Color: Brown, gray, or tan with visible shell fragments; Luster: Dull or earthy; Crystal structure: Amorphous/clastic; Cleavage: None (friable/fragmentary); Specific Gravity: 2.3-2.5
Formation & geological history
Formed in high-energy marine environments where shell fragments and coral debris accumulate. This specimen likely dates from the Pleistocene or Holocene epochs, often associated with coastal deposition in reefs or beach ridges.
Uses & applications
Used primarily in construction as a road base material, in landscaping, and historically as a sturdy building stone due to its ability to absorb cannon fire (notably in the Castillo de San Marcos). Specimens are also popular for basic educational fossil collections.
Geological facts
Coquina is composed almost entirely of broken shells and coral fragments. Because it remains relatively soft and porous when first quarried, it was famous in colonial Florida for being easy to cut into blocks and exceptionally durable against military bombardment.
Field identification & locations
Identify in the field by looking for a 'crunchy' texture composed of small shell bits; it will usually sizzle (effervesce) if a drop of vinegar or weak acid is applied. Commonly found along the Atlantic coast, particularly in Florida, the Carolinas, and the Caribbean.
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