Coquina
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Mineral NameCoquina
Chemical FormulaPrimarily CaCO3 (calcium carbonate)
Mohs Hardness3
Streak ColorWhite
CleavageNot applicable (sedimentary rock)
FractureUneven to irregular
Specific Gravity2
Colorstan, brown, off-white, yellowish-brown
TransparencyOpaque
Type LocalityFlorida, USA; many coastal regions worldwide
Mineral GroupSedimentary rock (bioclastic limestone)
Usesbuilding material, road aggregate, fertilizer, aquarium substrate
Associated Mineralscalcite, aragonite, quartz, clay minerals
Raritycommon
Description
A weathered pebble of coquina, primarily composed of fragmented bivalve shells cemented together. The surface is rough and bumpy due to the partial weathering out of the shells from the soft, tan-colored matrix.
Geological Context
Coquina forms in high-energy marine environments, such as beaches or shallow offshore areas, where wave action concentrates shell fragments and then cements them together, often rapidly.
