Geological Exploration of Metro Cleveland (GEM-C)

The Geological Exploration of Metro Cleveland tour is a series of Earthcaches which help to illustrate some geology that is hidden within the urban downtown area of Cleveland. These urban earthcaches help to highlight a wide variety of geological topics that are hidden in plain sight - in fact thousands of people walk by these stones every day without so much as a second thought about their origins!

This tour does not need to be done in any particular order and each earthcache is a standalone lesson. As you wander through the streets of Cleveland take a moment to pause and reflect on the lessons you can learn in just a normal city block!

As with all earthcaches there is no container to find here, rather you must read through the description below and answer a few questions in order to log this cache as found. Please ensure that you send your answers to the CO via email or message in a timely fashion.

Tears of Travertine

You are standing in the plaza of the PNC Center (formerly the National City Center Building). This building is clad in a white stone known as Travertine. Travertine is one of the most common building stones in the world and it's valued for its pristine color and overall durability. The name travertine is derived from the Latin phrase for "stone of Tibur," referring to the city in Italy in which the rock was quarried. This city is now known as Tivoli. The travertine for this building is Quaternary in age and was quarried in the Ditta Mariotti Prima Quarry in Tivoli. Travertine was chosen for this building because of its low cost compared to other good building stone, its light color (matching the tone of some nearby buildings), its uniform nature, and its lasting qualities. Slabs of the travertine, 2 to 3 cm thick, are anchored to the frame of the building with stainless-steel clip angles and pins. There is a 11/4-inch air space between the travertine facing and the enclosing wall of the building, designed to prevent water which collects behind the facing from being pulled into the building due to differential pressure.

Travertine is formed by the chemical precipitation of calcium carbonate minerals from fresh water, typically in springs, rivers, and lakes. When water that is high in CO2 concentration flows over a rock that has a lot of calcium carbonate (like limestone) it creates a weak acid that leaches some of that calcium carbonate into the water solution. When the water enters an area that has a lower CO2 concentration, it will deposit that calcium carbonate in thin layers - these layers build up over time and form travertine.

This chemical process is reversible and sometimes you can see trails of travertine emanating from travertine panels where water has dissolved portions of the calcium carbonate into a solution that then reforms as it passes a non-travertine location. At this location you'll use this knowledge to see if you can spot any examples of this travertine dissolution process. (Hint, look at the windows). These trails are a microcosm of how travertine forms in nature.

Logging Tasks:

QUESTION 1. Do you see any examples of calcium carbonate deposition? Describe them.

QUESTION 2.  Given your answer to question 1, do you suppose that the water this building is exposed to is slightly acidic, or slightly basic? 

Additional Logging Requirement: Post a photo that readily indicates that you (and anyone else logging the find) are at the building. This photo may be of yourself in front of the building, or it may be of a personal item!

References:

1. https://dam.assets.ohio.gov/image/upload/ohiodnr.gov/documents/geology/GB5_Hannibal_1992.pdf
2. https://en.wikipedia.org/wiki/Travertine​