Only Attempt this Cemetery EarthCache between Dawn and Dusk! Absolutely NO Night Caching!
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George J. Herter served in the U.S. Navy during World War II and the Korean War.
William W. Sampson served in the U.S. Army during World War II.
Find these two grave markers for the Earth Science lesson below. To help you find them, George Herter's grave is just east of William Sampson's. They both have flat VA headstones, but are made out of two different materials.
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Marble is a metamorphic rock consisting of carbonate minerals that recrystallize under the influence of heat, pressure and aqueous solutions, most commonly calcite or dolomite and has a crystalline texture of varying thickness. Marble is typically not foliated (layered), although there are exceptions. In geology, the term marble refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone. Marble is commonly used for sculpture and as a building material.
Granite is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions. Granite is typical of a larger family of granitic rocks that are composed mostly of coarse-grained quartz and feldspars in varying proportions. These rocks are classified by the relative percentages of quartz, alkali feldspar, and plagioclase, with true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals, though a few contain almost no dark minerals. Granite is nearly always massive, hard, and tough. These properties have made granite a widespread construction stone throughout human history.
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Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. Once a rock has been broken down, a process called erosion transports the bits of rock and mineral away. No rock on Earth is hard enough to resist the forces of weathering and erosion. Weathering and erosion constantly change the rocky landscape of Earth. Weathering wears away exposed surfaces over time. The length of exposure often contributes to how vulnerable a rock is to weathering. Rocks, such as lavas, that are quickly buried beneath other rocks are less vulnerable to weathering and erosion than rocks that are exposed to agents such as wind and water. Weathering is often divided into the processes of mechanical weathering and chemical weathering. Biological weathering, in which living or once-living organisms contribute to weathering, can be a part of both processes.
Mechanical Weathering, also called physical weathering and disaggregation, causes rocks to crumble. Water, in either liquid or solid form, is often a key agent of mechanical weathering. For instance, liquid water can seep into cracks and crevices in rock. If temperatures drop low enough, the water will freeze. When water freezes, it expands. The ice then works as a wedge. It slowly widens the cracks and splits the rock. When ice melts, liquid water performs the act of erosion by carrying away the tiny rock fragments lost in the split. Temperature changes can also contribute to mechanical weathering in a process called thermal stress. Changes in temperature cause rock to expand (with heat) and contract (with cold). As this happens over and over again, the structure of the rock weakens. Changes in pressure can also contribute to exfoliation due to weathering. In a process called unloading, overlying materials are removed. The underlying rocks, released from overlying pressure, can then expand. As the rock surface expands, it becomes vulnerable to fracturing in a process called sheeting. Another type of mechanical weathering occurs when clay or other materials near rock absorb water. Clay, more porous than rock, can swell with water, weathering the surrounding, harder rock. Salt also works to weather rock in a process called haloclasty. Saltwater sometimes gets into the cracks and pores of rock. If the saltwater evaporates, salt crystals are left behind. As the crystals grow, they put pressure on the rock, slowly breaking it apart. Honeycomb weathering is associated with haloclasty. As its name implies, honeycomb weathering describes rock formations with hundreds or even thousands of pits formed by the growth of salt crystals. Honeycomb weathering is common in coastal areas, where sea sprays constantly force rocks to interact with salts. Haloclasty is not limited to coastal landscapes. Salt upwelling, the geologic process in which underground salt domes expand, can contribute to weathering of the overlying rock. Plants and animals can be agents of mechanical weathering. The seed of a tree may sprout in soil that has collected in a cracked rock. As the roots grow, they widen the cracks, eventually breaking the rock into pieces. Over time, trees can break apart even large rocks. Even small plants, such as mosses, can enlarge tiny cracks as they grow. Animals that tunnel underground, such as moles and prairie dogs, also work to break apart rock and soil. Other animals dig and trample rock aboveground, causing rock to slowly crumble.
Chemical Weathering changes the molecular structure of rocks and soil. For instance, carbon dioxide from the air or soil sometimes combines with water in a process called carbonation. This produces a weak acid, called carbonic acid, that can dissolve rock. Carbonic acid is especially effective at dissolving limestone. When carbonic acid seeps through limestone underground, it can open up huge cracks or hollow out vast networks of caves. Another type of chemical weathering works on rocks that contain iron. These rocks turn to rust in a process called oxidation. Rust is a compound created by the interaction of oxygen and iron in the presence of water. As rust expands, it weakens rock and helps break it apart. Hydration is a form of chemical weathering in which the chemical bonds of the mineral are changed as it interacts with water. One instance of hydration occurs as the mineral anhydrite reacts with groundwater. The water transforms anhydrite into gypsum, one of the most common minerals on Earth. Another familiar form of chemical weathering is hydrolysis. In the process of hydrolysis, a new solution (a mixture of two or more substances) is formed as chemicals in rock interact with water. In many rocks, for example, sodium minerals interact with water to form a saltwater solution. Living or once-living organisms can also be agents of chemical weathering. The decaying remains of plants and some fungi form carbonic acid, which can weaken and dissolve rock. Some bacteria can weather rock in order to access nutrients such as magnesium or potassium. Clay minerals, including quartz, are among the most common byproducts of chemical weathering. Clays make up about 40% of the chemicals in all sedimentary rocks on Earth.
Weathering and People: Weathering is a natural process, but human activities can speed it up. For example, certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they change into acids. They then fall back to Earth as acid rain. Acid rain rapidly weathers limestone, marble, and other kinds of stone. The effects of acid rain can often be seen on gravestones, making names and other inscriptions impossible to read. Acid rain has also damaged many historic buildings and monuments.
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Marble is made of limestone, whereas granite is made of igneous rock. The sediment rock that marble is made from means it reacts to acids and may be soft enough to be scratched using the blade of a knife. Marble also comes in a range of colors that are displayed in swirling patterns on the stone.
The igneous rock that makes up granite has been formed via the solidification of magma, creating a tough and durable rock. This rock will last through whatever Mother Nature throws at it, from rain and sleet to snow. It is scratch resistant as well. Granite is resistant to both water and heat. The color variation in granite is evident in the color flecks on the stone.
The biggest difference between granite and marble is that granite is much harder and lasts much longer than the softer marble. Marble is more likely to crack, chip and erode over time due to being exposed to the outdoor elements. In a few decades, an inscription on a marble tombstone may be difficult to read. On the other hand, granite tombstones can withstand severe weather and will appear almost identical decades in the future.
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Find the two grave markers at the posted coordinates...the coordinates should bring you right between the two. Your goal is to study the difference in weathering between the marble and granite grave markers. Take a close look at both stones, noting the color, the size of the grain of the minerals in each, and the weathering. Although George Herter's grave marker was placed over two decades after William Sampson's, you will find the weathering on each to be very interesting for their age.
Send me the answers to the following questions, and post a photo (required):
- Standing back at a distance, what is the biggest difference in the color of Herter's grave stone versus Sampson's?
- Looking closely at the two grave stones, can you see visible minerals in the two stones? What colors do you see in each, if any?
- Describe the difference in weathering between the two stones. Does one seem to be eroding faster than the other? What conditions do you believe are causing this here?
- Based on your observations, and knowing that one stone marker is about 24 years older than the other, how much more often do you think the marble marker will need to be replaced because of weathering?
- Post a photo of yourself, your group, or something that identifies you in the cemetery.
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Sources:
The Archaeology of American Cemeteries and Gravemarkers, Sherene Baugher & Richard Veit, 2016
Rock Identification Field Guide, Patrick Nurre, 2014
