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Pictures of Sedimentary Rock Types


Coquina ("co-KEEN-a") is a limestone composed chiefly of shell fragments. It's not common, but when you see it you want to have the name handy. (more below)
Keep the name handy
Copyright Linda Redfern, used by permission
Coquina is the Spanish word for cockleshells or shellfish. Coquina forms near shore, where wave action is vigorous and sorts the sediments well. Most limestones have some fossils in them, and many have beds of shell hash, but coquina is the extreme version. A well-cemented, strong version of coquina is called coquinite. A similar rock, composed chiefly of shelly fossils that lived where they sit, unbroken and unabraded, is called a coquinoid limestone. That kind of rock is called autochthonous (aw-TOCK-thenus), meaning "arising from here." Coquina is made of fragments that arose elsewhere, so it is allochthonous (al-LOCK-thenus). Those are handy words in geology.

See more photos in the Coquina Gallery and the Sedimentary Rocks Gallery.

Other galleries:
Geologic Features and Processes
Glaciers and Ice
Geology and Society

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