Maryland's 9/11 memorial is located in downtown Baltimore near the entrance to the Maryland World Trade Center. It is composed of two peices. The base made of banded marble slabs while the top has an I-beam that was brought from the World Trade Center site in New York City sometime after the attacts. This earthcache will focus on the geologic aspect of the memorial, more specifcally the banded marble.
Marble is a micro-crystalline metamorphic rock, meaning it contains crystals that are too small to see with the naked eye. It formed deep within the earth. Its protolith rock (meaning the rock before it was metamorphosed into marble is limestone, a common sedimentary rock found close to the shore in costal marine environments. Limestone can contain fossils, but through the transformation process of creating metamorphic rock all remnants and structures of the fossils are lost.
Pure marble has a milky white color. However, if the protolith rock contains impurities (which is most of the time), then it can form bands. Banding can occur based on the variation in mineral content within the protolith rock. This variation, through the metamorphic process of heat, pressure, and time, can create bands of different colors and thicknesses.
Unpolished marble banding looks like this:
Their orientation(s) within the rock can tell us a lot about the principle stresses. For example, the maximum principle stress (called sigma-1 [or σ1]) is typically orientated in the north-south direction. In other words, it is orientated vertically in the same direction as the force of gravity. This makes sence as the weight of the rock above squeezes the rock below. However, if there are tectonic forces involved, it could complicate the orientation of sigma-1. There are other sigmas and orientations of stress, however, sigma-1 is always the orientation of where stress is greatest and therefore has the greatest effect on the orientation of banding, which is usually perpendicular (90 degrees) to this orientation (typically in the directions of sigma-2 and sigma-3).
Some common minerals include:
Works Cited
https://sites.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Marble.html
https://www.zigersnead.com/projects/details/9-11-memorial-of-maryland/
http://geologycafe.com/gems/chapter9.html
https://miningeology.blogspot.com/2015/05/metamorphic-ore-deposits.html
http://rogermarjoribanks.info/sense-movement-structures-part-1-theory/
1. "Maryland 9/11 Memorial" on the first line of your email (or message through the geocaching message center) AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails/message in the spirt of earthcaching.
2. Take a close up photo of the banding of the rock using some sort of scale. Geologists often use coins, GPS', pens, shoes, notebooks, ect. You might want to be creative in what you use for your scale, however, the scale that you choose is entirely up to you. Make sure your photo is close enough to capture bands that can be clearly seen. This photo MUST be uploaded to your "found it" log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
3. Describe the (a) texture(s) and (b) color(s) of the marble.
4. Using the mineral identification charts, name at least one mineral that is present within the bands AND one that is in the matrix of the marble.
5. Describe any weathering, rusting, or corrosion that may be occurring. If nothing is occurring, explain why this may be the case. If there is, explain why you think this is occurring.
6. As the marble is displayed now (not when it was forming), and based on the average orientation of the banding, is sigma-1 orientated vertically or horizontally? How can you tell? Explain.
