Nummulite

A nummulite is a large lenticular fossil, characterized by its numerous coils, subdivided by septa into chambers. They are the shells of the fossil and present-day marine protozoan Nummulites, a type of foraminiferan. Nummulites reaches 6 cm or 2.4 inches in diameter, and are common in Tertiary marine rocks, particularly around the Mediterranean (e.g. Eocene limestones from Egypt). They are valuable as index fossils.

The name "Nummulites" is a diminutive form of the Latin nummulus meaning "little coin", a reference to their shape. In 1913, Randolph Kirkpatrick published a book, The Nummulosphere: an account of the Organic Origin of so-called Igneous Rocks and Abyssal Red Clays, proposing the theory that all rocks have been constructed by the accumulation of forams such as Nummulites.