answer:oquina (co-KEEN-a) is a limestone composed chiefly of shell fragments. It's not common, but when you see it, you'll want to have the name handy.
Coquina is the Spanish word for cockleshells or shellfish. It forms near shorelines, where wave action is vigorous and it 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).