A Hammerless Geological Excursion Across North UGA Campus

Many buildings on our campus are constructed, in part from a variety of ornamental building stones. Most of these were taken from quarries here in Georgia, although stone from as far away as Indiana, Pennsylvania, and India can be found on campus.

Please meet at the ACADEMIC BUILDING on north campus

Stop 1. Study the steps on the east side of the ACADEMIC BUILDING. Most of the blocks used are structureless. They come from the Elberton batholith, about 50 miles east of here on Hwy. 72. Locate the one block with good xenoliths (fragments of the rocks surrounding the batholith; they fell into the pluton while it was still molten). The xenoliths are composed almost entirely of hornblende and plagioclase.

From your knowledge of metamorphic rocks, what rock name would you give the xenoliths?

What would a likely protolith be? _________________________________________

Note that some of the blocks contain light colored dikes. These dikes are composed of fine grained minerals and are called aplites. Aplites are commonly associated with the final stages of crystallization of granitic plutons such as the Elberton batholith. What minerals would expect in the aplite? ___________ __________

Another block in the steps shows a good foliation. This foliated block also comes from the Elberton batholith. What possible explanation can you think of to explain the structureless nature of most of the blocks and the good foliation in this one? _________________________________________________

Stop 2. Proceed west to the corner of Broad Street and Herty Drive Study the rock at the base of the brick pillars at the gate to Herty Dr.

What is the general color of the rock? _______________________________________
What is the pink mineral? _______________________
white mineral? _____________
black mineral? ____________________
clear glassy mineral? ___________________
What is the texture of the rock? __________________________________________
What name would you give the rock? _____________________________________

Stop 3. Continue south, past Demosthenian Hall, and examine the floor behind the colonnade of the CHAPEL.

What is the main texture and fundamental rock type of this stone?________________________
What is the main mineral present in this rock? ______________________________________
What rock name would you give this stone? ________________________________________
Use a hand lens to examine the small dark mineral grains which stand out in relief. They are reddish brown, form small neat
crystals and show abundant crystal faces. They have a hardness of 7 and have no cleavage (thus are resistant to weathering).
What is this mineral? __________________________________________________
Some slabs of this rock show a pronounced lineation, caused by millimeter scale folding of the foliation. Examine this
carefully.
Your answer to question 3(a) should set off another question, namely; what is the likely protolith for this rock?
______________________________________________

Stop 4. Proceed west to the Old College, examine the monument to Abraham Baldwin. Note the well developed interlocking crystalline texture of the rock on the top of the monument where the acid rain has etched the stone, revealing its texture.

• What is the rock type? ___________________________
• Unpolluted rainfall has a slightly acidic pH of 5.6; acid rain often reaches a pH as low as 4.2, thereby accelerating the weathering of calcite. The east and south sides of the monument have some irregularly shaped darker streaks, which probably represent highly deformed bedding surfaces where clays and organic matter once settled onto the carbonate sediments. Later, metamorphism of this rock was accompanied by strong deformation which folded the rocks and produced the irregular streaks by variable amounts of movement along cleavage surfaces. (Compare this rock with the marble in the internal stairway in the GGS building). Based on what you know about metamorphism of clays and organic matter, what minerals do you think produce the dark color of the streaks? ________________
• Inspection of the plaques on the north side of the building reveals that Old College is oldest building, constructed in 1806. A marble marker that contains a list of names (probably trustees who approve the building) reveals a date of 1801. A smaller plaque below is less weathered than the 1801 plaque and reads that extension wall were renovated in 1908 with appointment by the legislature. The Bladwin monument was erected in 1942 by the Department of Natural Resources Division of State Parks and Historic Sites and Monuments and by the Georgia Society of Daughters of American Colonists. If you are now wondering about the rates of chemical weathering, than this historical data provides dates (1801, 1908, 1942 and Today) for a study of the same Tate marble. From such a study, one can predict the "half-life" of a marble constructed monument in Athens, GA.

Stop 5. Proceed to the Main Library, going past the new Law School on your right. Further south, examine the columns in front of the Old Law School Building. Using a hand lens, examine the rock where it has been bruised and is not polished. Notice several types of fossil fragments, including many very thin shells seen on edge. These produce the long thin white fragments often lined up nearly parallel to the vague bedding planes which can be detected after careful inspection of the columns.

• What rock name would you give this rock? _______________________________
• Is it of clastic or chemical origin? _______________________________________

Stop 6. Proceed to the Main Library. Walk along the west wall of the library. The bottom 3 or 4 meters of the wall is made of blocks of stone which probably come from Indiana. Examine the rock with a hand lens.

• What is the structure visible in most of the blocks?__________________________
• What features make this structure visible?_________________________________
• From the presence of this structure and the nature of the rock you have examined here, what would you conclude on the general classification of this rock?________________________________________________________________________
• Name the rock. _______________________________________________________________
• In the middle of the west wall, you we one block with a rusty vein across it. The vein material is a sulfide mineral, pyrite or marcasite (both are FeS₂) Rain and humidity attack pyrite, forming an acid. Can you name the acid formed? ___________________________________________________________________________
• What would you conclude regarding the suitability of a stone with abundant pyrite veinlets as a construction material? _________________________________________________________

   

Stop 7. Proceed back to the front of the Main Library. Note the gray pillars and walls with the interesting structures.

• What is the name of this structure? ___________________________________________
• Based on what you know from lecture, what would you name this rock? _____________
• Go to the small stairway to the right of the main entrance and examine the large slab on the top of the doorway. It is typical of a rock called "migmatites" from the Lithonia area quarries. You can see many small faults that are 'healed' in the process of "migmatization", which took place at a pressure and temperature very close to the point at which this rock completely melts. You can see that portions of this rock were melted and behaved like an igneous melt, where other portions (generally darker and more biotite-rich) were more like plastic and were folded.
• * Optional - Go into the rest rooms and examine the marble slab (quarried near Tate, Georgia) which separates the toilets. Notice the relict bedding, similar to what you saw at the Abraham Baldwin monument. The rock has been tightly folded. Watch for the traces of foliation planes, which bisect the angles formed by the limbs of the folds. Make a quick sketch of the folded layers and the foliation surfaces.