An Ordovician limestone called "Tennessee Marble" in the Tennessee State Supreme Court building
Building Image
 
      The building above is the Tennessee State Supreme Court building in Nashville, Tennessee. It is built of limestone (more specfically, a bioclastic grainstone) from the Ordovician-age Holston Formation in eastern Tennessee. The surface of the rock on this building has been etched sufficiently by acidic rainwater that the bioclastic grains are quite evident, so that one can see that this is defintely a limestone - it retains the fossiliferous texture that would be lost in metamorphism. The stone is nonetheless marketed as "Tennessee Marble" from quarries around Knoxville, because it polishes to a shiny pinkish-brown.

 
      One of the striking features of this limestone is its stylolites, the zig-zag roughly horizontal lines cutting across the stone in the image below, and shown in more detail in the second image down. Styolites are surfaces generated by pressure dissolution, a process in which CaCO3 (in this case, calcite) dissolves along certain horizons, leaving behind a residue of insoluble minerals. Those insoluble minerals are typically darker than the calcite, so that the stylolite shows up as a dark zig-zig line against the white rock. The zig-zag nature of the line develops because the dissolution process varies in rate along opposite sides of the stylolite. (For more about stylolites, you can see the Atlas of Pressure-Dissolution Features.

 
Stone Image
 
Stone Image
 
      As noted above, the stone on the outside of the building has been etched, and it has been bleached white by weathering. Weathering has also preferentially attacked the stylolites, so that they have receded into the rock. The image below shows a polished fresh piece of the same limestone. Note the darker color and the clearer definition of the stylolites. (The image is about 4 inches or 10 centimeters across, and so about 2.5x on most computer screens.)

 
Sample Image
 
 
      Finally, we should note that visitors to the Tennessee State Supreme Court building will see more than just limestone outside. The front patio shown below consists of a gray granite with large sheets of brown limestone. The lower course of stones of the building itself is also granite.

 
Patio Image

 


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