English: Limestone from the Mississippian of Indiana, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)

Limestone is a biogenic sedimentary rock composed of calcium carbonate - usually calcite. Some limestones are composed of aragonite, a polymorph of calcite (e.g., most of the bedrock on Bahamian islands).

The sample shown here is "Indiana Limestone", a retail name for building stone-grade rocks in the Salem Limestone, a Mississippian-aged unit in Indiana. The rock itself ids well sorted - it's principally sand-sized fossil fragments ("fossil hash") (click on the photo to zoom in & look around - individual grains can be discerned). Limestones composed of sand-sized grains are called calcarenites ("arenites" are sandstones).

The slightly brownish-colored layering present in this specimen represents depositional bedding and laminations.

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From exhibit signage:

Indiana Limestone

Often called the most famous building stone in North America, this homogeneous gray limestone of Mississippian age has been quarried for many years in the Bloomington region of southern Indiana. Many buildings throughout the Midwest are constructed of this stone.

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Stratigraphy: Salem Limestone, Middle Mississippian

Locality: unrecorded/undisclosed site (probably a quarry) in southern Indiana, USA