Thursday, November 02, 2023

Geologic State Symbols Across America - Indiana

 The next state up for the Geological State Symbols Across America is:


You can find any of the other states geological symbols on my website here: (being updated as I go along).

                                                                                       Year Established
State Stone: Limestone                                                                     1971

State Stone: Limestone

IC 1-2-9-1
Sec. 1. The regal type rock "Limestone" which is found and quarried in south and central Indiana from the geologic formation named the Salem Limestone, is hereby adopted as the official stone of the State of Indiana.
(Formerly: Acts 1971, P.L.3, SEC.1.)
Salem Limestone quarry. Photo by Teal Strabbing courtesy of

Limestone is one of the main sedimentary rocks, along with sandstone and shale. Limestone is often formed from the carbonate shells of aquatic animal life, since most shelly animals makes their shells out of a variety of carbonates (CaCO3). One of the hallmarks of carbonates is that they react with acid, making limestones fairly easy to identify as a whole. However there are multiple varieties of limestones depending on where there were formed, what their primary mineral is, the size and types of the fossils within the limestone, and what type of cement is present within the rock. These include fossiliferous limestone, coquina, chalk, micrite, crystalline limestone, oolitic limestone, and travertine. Fossiliferous limestone is formed usually on the continental shelf from the large shells of animals like clams and snails cemented together with microscopic calcium carbonate shells, called lime mud. Coquina is typically formed in beach like environments where the number of animal shells far exceeds the surrounding sediment. Although some definitions vary, the typical definition is that coquina is made up of loosely cemented shells with little to no matrix (cement). Chalk is formed from the compaction of microscopic plates called coccoliths, which come from animals called coccolithophores. Chalk is similar to fossiliferous limestone except the rock is typically all white and contains only one type of fossil. Micrite is comprised primarily of lime mud, like a fossiliferous limestone without the fossils. It forms a little further out from the shoreline than fossiliferous limestone where the mud can float out in the water but is generally too deep for shelled animal life. Crystalline limestone is an inorganic type of limestone that usually forms in shallow lagoons or lakes. The water in the lagoon becomes saturated in calcite and then the water starts to evaporate causing calcite to precipitate out of the rock. This is common where water is periodically added to a lagoon or a lake after a lot of calcite is precipitated out. It is also found when other types of limestone are altered in some way. Oolitic limestone is another inorganic type of limestone where limestone mud is deposited along the continental shelf edge and the naturally movement of the water rolls the mud around creating little balls of calcite. These little calcite balls are then cemented together. And the last limestone variety, travertine, is formed in caves from the deposit of calcite along stalactites, stalagmites, and other flowstones. Since the structures are built up layer by layer, this causes the rocks to often have a banded appearance with often a lot of holes within it.

Salem Limestone Quarry locations. Image courtesy of CUNY - Brooklyn College.

Although the State Stone is designated a "Limestone", the official state announcement calls out specifically the Salem Limestone from the south and central Indiana, so we will focus on that limestone in particular. Due to incomplete knowledge of the extent of the Salem Limestone deposits when it was first being quarried, the body currently known as the Salem Limestone has gone through many names throughout history. These include the Bedford stone, Bloomington stone, Ellettsville stone, Salem stone, White River stone, Bastard stone, Bedford Marble, Gosport Stone, Indiana Oolitic Stone, Spergen fossil bed, Bedford Oolitic Limestone, Spergen Hill Limestone, Spergen Limestone, Salem Formation, and the Indiana Limestone (of which it is known today in the building-stone trade). 

Salem Limestone. Image courtesy of

The Salem Limestone is a Middle Mississippian age (335-340 million year old) light-grey to bluish-grey pure calcarenite limestone that crops out between Bloomington and Bedford in the south-central portion of Indiana. It formed in a shallow sea that straddled the equator at the time. Wave action broke up the largest particles creating a limestone that consisted mostly of smaller fossil fragments. This wave action also produced quite a bit of cross-bedding throughout the deposit as well. Quarrying of the stone began in 1827 and has continued up to the present day with nine different quarries all mining the same formation. Indiana Limestone is a "freestone", which means that there is no preferential cracking, jointing, or splitting. This also means that blocks of the limestone can be planed, hand-worked, or otherwise manipulated without fear of the rock breaking in a preferential direction. The limestone is 97% pure calcite with microscopic foraminifera and bryozoan fossils found throughout. Other fossils that can be found in limited quantities include gastropods, pelecypods, brachiopods, and crinoids. The Salem Limestone has been used as a building stone in many famous projects across the country including the Lincoln Memorial, the Thomas Jefferson Memorial, Grand Central Station, Ellis Island, the Empire State Building, The Pentagon, and 27 U.S. state capitol buildings. This abundance of use and it's beautiful appearance has made this "The Nation's Building Stone".


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