Tennessee marble is a type of crystalline limestone found only in East Tennessee, in the southeastern United States. Long esteemed by architects and builders for its pinkish-gray color and the ease with which it is polished, this stone has been used in the construction of numerous notable buildings and monuments throughout the United States and Canada, including the National Gallery of Art and the National Air and Space Museum in Washington, D.C., the Minnesota State Capitol, as well as parts of the United States Capitol in Washington, Grand Central Terminal in New York, and Union Station in Toronto. Tennessee marble achieved such popularity in the late-19th century that Knoxville, the stone's primary finishing and distribution center, became known as "The Marble City."