Honoring the spot where John Fitzgerald Kenedy announced his candidacy for the presidency in West Virginia, the JFK memorial serves as a reminder of a father's love and hope for the future. This piece was done by artist Chris Kroll in 2007. It is a homage to fatherhood and includes a bronze statue depicting John F. Kennedy Jr. saluting his father’s casket in 1963, and a base relief of President Kennedy. A 27-foot wide memorial featuring bronze statues of JFK and John Jr., three tall granite pillars, and a granite bench as you walk near the riverfront on the Rail Trail in Star City. Reference.
What is Granite?
For thousands of years, granite has been one of mankind's first choices for creating buildings and monuments from stone. Granite is the most abundant rock on Earth, making up about 75% of the Earth's crust. Quarrying and working with granite has never been easy, as it is exceptionally hard, durable, and resistant to the elements...the same qualities that make it a great material for buildings and monuments. Reference.
How is Granite Formed?
Granite rocks are igneous rocks formed by slowly cooling pockets of magma trapped beneath the earth's surface. Igneous rocks form from molten rock which is either ejected at the surface of the earth or cools underground. Igneous rocks make up 95% of the rocks of the earth's crust. They are also some of the oldest rocks found at the surface of the earth. Igneous rocks are classified based on where they form and the composition of the molten rock. Magma originates from the melting of the earth's crust and upper mantle. This melting occurs around a depth of 20 to 140 miles below the earth's surface. As pockets of magma cool slowly underground, the magma becomes an igneous rock. This molten rock is less dense than the solid rock, so it rises towards the surface. Molten rock that cools before it reaches the surface hardens to become intrusive igneous rock. Because it forms deep beneath the earth's surface, it has more time to cool and develop large crystals. Intrusive rocks include granite.
An intrusive rock means that molten rock cooled within the crust and was never expelled as molten rock. The gradual cooling of molten rock is imperative to create the large crystals of a singular mineral that we see in granite. With time, there is differential lithification or solidifying of molten rock dependent on chemical makeup, this allows for different types of minerals to form at different periods and alter the final resulting granite. Therefore, the size of individual grains is proportional to how slowly the molten rock was cooled. Extrusive rocks cool during a volcanic eruption and allow no time for the orientation of minerals, creating a homogenous-looking rock with no discernible grains. Reference.
The Minerals of Granite
The minerals which make up granite are composed of silicon and oxygen. Granite is made out of big crystals; you can easily see them with the naked eye. This is because the granite cooled slowly underground, shielded by the rock surrounding it so that its great heat could escape slowly. Granite is mostly made out of feldspar and quartz, plus minor amounts of other minerals. Feldspar and quartz are light minerals. Therefore, when hot molten rock comes up from the mantle, some minerals grow crystals and then later, others form. If the magma (liquid rock) keeps moving, those early crystals are left behind, until finally what are left are mostly the ingredients for feldspar and quartz. The result: granite.
Granite is a conglomerate of minerals and rocks, primarily quartz, potassium feldspar, mica, amphiboles, and trace other minerals. Granite typically contains 20-60% quartz, 10-65% feldspar, and 5-15% micas (biotite or muscovite). The minerals that makeup granite give it the unique colors we see in different types of granite.
The relative proportion of different colored minerals in granite is largely due to the source of molten rock that cooled to form the granite. If the molten rock was abundant in potassium feldspar, the granite is more likely to take on a salmon pink color. On the other hand, if the molten rock is abundant in quartz and minerals that make up amphibole, you will likely get a black and white speckled granite.
The combination of the minerals below makes up most of the colors we typically see in granite:
- Quartz - typically milky white color
- Feldspar - typically off-white color
- Potassium Feldspar - typically salmon pink color
- Biotite - typically black or dark brown color
- Muscovite - typically metallic gold or yellow color
- Amphibole - typically black or dark green color
White granite is a granite that is composed primarily of quartz (milky white) and feldspar (opaque white) minerals. Pink-colored granite is a result of an abundance of potassium feldspar within the granite. Black and White Granite has equal parts quartz, feldspar, and amphibole, making a speckled black and white granite. Red granite is a variation of pink potassium feldspar abundant granite, where the k-feldspar takes on a redder-than-pinker color. Also, you can get red coloring from iron oxide in hematite grains or inclusion within feldspar, essentially the same process that makes rusted metal red colored. Reference.
The Weathering of Granite
Weathering is a necessary precursor for rock development. However, in the context of granite, it acquires a particular importance for various reasons. First, many granite terrains show an extensive development of deep weathering profiles, which can be extremely varied in terms of their depth, vertical zonation, degree of rock decomposition, and mineralogical and chemical change. Moreover, the transitional zone between the weathering mantle and the solid rock, for which the term ‘weathering front’ is used, may be very thin. There is now sufficient evidence that many geomorphic features of granite landscapes, including boulders, domes, and plains, have been sculpted at the solid rock/weathering mantle interface and they are essential elements of an exposed weathering front. Therefore, the origin of granite landscapes cannot be satisfactorily explained and understood without a proper understanding of the phenomenon of deep weathering. Second, granites break down via a range of weathering mechanisms, both physical and chemical, which interact to produce an extreme diversity of small-scale surface features and minor landforms. In this respect, it is only limestones and some sandstones that show a similar wealth of weathering-related surface phenomena. Third, both superficial and deep weathering of granite act very selectively, exploiting a variety of structural and textural features, including fractures, microfractures, veins, enclaves, and textural inhomogeneities. In effect, the patterns of rock breakdown may differ very much between adjacent localities, and so the resultant landforms differ. In the context of deep weathering, selectivity is evident in significant changes in profile thickness and its properties over short distances, and in the presence of unweathered compartments (corestones) within an altered rock mass. Fourth, it is emphasized that granites are particularly sensitive to the amount of moisture in the environment. They alter very fast in moist environments, whereas moisture deficit enhances rock resistance and makes it very durable. Hence, a bare rock slope shedding rainwater and drying up quickly after rain will be very much immune to weathering, whereas at its foot a surplus of moisture will accelerate decomposition. Reference
Questions!
Once at the posted coordinates, please make some observations based on the information shown above to describe the geological significance of the JFK Memorial monument. Once you are satisfied with your observations, please submit your answers to the CO.
1. Looking at the granite, what combination of minerals are present based on the color?
2. Run your hands along the side of the memorial. Describe the texture, compared to the front, and use the information in the description to describe what is happening. Do you think being next to the river impacts this geological phenomenon?
3. Looking at the Star City Veterans Memorial next to the Kenenedy Memorial, do you think that this stone is also quarried from Georgia Grey Granite?
4. (Optional) Post a picture of yourself at GZ during your visit.
Special thanks to Awesnap for helping me develop the information and questions for this earthcache!
