Limestone

Limestone is a sedimentary rock composed primarily of calcite, a calcium carbonate mineral. It is formed from the accumulation of shells, coral, and other organic debris in marine environments. Limestone is a popular choice for architectural applications due to its versatility, durability, and its aesthetic appeal. 

Much of the limestone used in Chicago architecture is Indiana Limestone. It is a fine-grained, light-colored limestone that is known for its durability and ease of carving. Indiana limestone is characterized by its warm, earthy tone and its ability to weather gracefully over time. Bedford Limestone, another popular type of limestone used in Chicago, is a medium-grained, gray-brown limestone that is also known for its strength and durability. Bedford stone is often used for exterior cladding and architectural details. 

While limestone is used for exterior cladding, it is also utilized in interior finishes, sculptures and monuments as well as decorative architectural details such as columns, capitals, and moldings.  

EXAMPLES IN CHICAGO:  

1. The Palmer House: This historic hotel, a Chicago landmark, uses limestone for its exterior cladding and interior finishes. 
2. The Field Museum: The museum's exterior is clad in limestone, giving it a solid and imposing appearance. 
3. The Chicago Board of Trade Building: The building's exterior is adorned with limestone columns and other decorative elements.