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Earthcache about Monument Stones in Greenlawn Cemetery
This Earthcache examines the effects of weathering on gravestones made of different materials. As this cache is located in Greenlawn Cemetery, please be respectful of the area and only visit during the daylight hours. Enter off of Lila Avenue or Cemetery Road. Permission for this Earthcache has been granted by the site manager of Greenlawn.
Standing in the driveway at the posted coordinates, facing east, you will notice two nearby obelisk gravestones. The one on the left (north) is made of marble on a limestone base, and marks the grave of Jacom Armstrong, who died in 1875. The one on the right (south) is made of grey granite on a limestone base, and marks the grave of Amelia (d. 1870) and John D. (d. 1906) Gatch. Two stones, of reasonably similar age, design, and height, but made of different stones. Yet, one is noticeably more weathered than the other. Why?
What is Weathering?
According to Merriam Webster Dictionary, weathering is “the action of the weather conditions in altering the color, texture, composition, or form of exposed objects; specifically : the physical disintegration and chemical decomposition of earth materials at or near the earth's surface.”
There are two basic classifications of weathering processes – physical and chemical weathering; and each can involve biological or non-biological components.
Physical weathering, also called mechanical weathering, is the class of processes that causes the weathering of rocks without chemical change. The primary process in physical weathering is abrasion. Thermal stress weathering occurs when temperature changes cause the expansion and contraction of rock. Frost weathering occurs when water seeps into cracks in the rock, then expands and contracts as the water freezes, exerting pressure on the surrounding rock. Wind can carry sand and other sediments, which over time can wear away the surface of rocks. Plant roots sometimes get into cracks in rocks and pry them apart, resulting in disintegration.
Chemical weathering changes the chemical composition of rocks, often when water interacts with minerals to create various chemical reactions. One of the most common chemical weathering processes is carbonation, where atmospheric carbon dioxide reacts with chemicals in the rock. Carbonation occurs on rocks which contain calcium carbonate, such as limestone and chalk. Acid rain also causes chemical weathering. A number of plants and animals may create chemical weathering through release of acidic compounds. Lichens, algae, and moss all produce various chemical compounds that can react with chemicals in some rocks.
The Properties of Different Rocks Used for Gravestones
The most common materials used for gravestones in this cemetery include granite, marble, limestone, slate, and sandstone. Granite and limestone are not native to the area; these stones were imported from elsewhere. Limestone, slate, and sandstone are quarried locally, although gravestones made from these materials can be from local or imported stone.
Granite is an igneous rock which consists mainly of quartz, mica, and feldspar. It is granular in texture, and can be pink to gray in color, depending on their chemistry and mineralogy. Granite is hard and tough, and therefore it has gained widespread use as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3.
Marble is a metamorphic rock composed of recrystallized limestone. Marble is commonly used for sculpture and as a building material. Marble has been used in sculptures, buildings, and gravestones since classical times. This is due to its softness, which makes it easy to carve, its relatively homogenous consistency, and a resistance to shattering.
Slate is a fine-grained, foliated metamorphic rock that comes from an original shale-type sedimentary rock composed of clay or volcanic ash. Slate is foliated, or layered. It commonly is formed in layers that can be split or broken apart. Because of this foliation, slate is commonly used to make roofing tiles. Due to its resistance to heat and its chemical inertness, slate has been used for laboratory bench tops. In areas where it is available, high-quality slate is often used for tombstones.
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite. Many limestones are made from the skeletal fragments of marine organisms such as coral or foraminifera. Like most other sedimentary rocks, most limestone is composed of grains, making it somewhat porous. Limestone was a popular building material in the late 19th and early 20th centuries. The Bloomington, Indiana area has long been a source of high quality quarried limestone, and much of the limestone used in the Cincinnati area came from Bloomington. Limestone and marble react with acid solutions, making acid rain a significant problem to the preservation of gravestones made from them.
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Sandstone is usually very porous, which allows percolation of water and other fluids. Sandstone was commonly used for headstones because it was inexpensive, available locally, and easy to carve. Unfortunately, because of its porous nature, sandstone headstones are especially prone to damage due to weathering.
Logging This Earthcache
In order to log this Earthcache, examine the marble Armstrong obelisk and the granite Gatch obelisk, and email the answers the following questions:
- Examine the lettering and edges of each stone. Is one easier to read than the other? Which obelisk shows more signs of weathering?
- Examine the texture of the flat surfaces of each stone. Is one smoother than the other? Does one have more cracks or other textures that would allow water to seep in? Do you think the texture has affected the amount of weathering on each stone?
- Examine the limestone bases of each obelisk. How have the bases weathered differently than the rest of the obelisks?
- Are there signs of biological factors that would cause weathering on either obelisk? If so, what are they?
- EXTRA CREDIT: Examine the slate headstones to the immediate left (north) of the Armstrong obelisk. Compare the effects of weathering on these stones with the weathering of the obelisks.
Photos are welcome, but not required. We also encourage you to stroll the grounds and visit the graves of others, including former Ohio governor John M. Pattison, whose granite monument is just a few yards east of the posted coordinates, near the center of Section 7. The nearby flagpole has a plaque with more information about him. There are also stones of a variety of materials and unique designs.
Milford GeoTrail:
Official GeoTrail Caches
MG00-Info & TB Hotel
MG01-Milford Fire Department
MG02-Greenlawn Cemetery
MG03-Garfield Park
MG04-Valley View
MG05-Terrell Park
MG06-Little Miami Scenic Trail
MG07-Long Stone Buildings
MG08-Old Town Hall
MG09-Row Houses
MG10-Critchell Park
MG11-Indian Mound
MG12-Promont
MG13-Masonic Lodge
Bonus caches
MGb2-Monument Stones at Greenlawn
MGb1-Milford Urban Trail
Benchmark "Welcome to Milford."
Events
Milford GeoTrail Event - Launch Party (May 3rd, 2014)
Milford OH GeoTrail CITO (May 3rd, 2014)
GeoTrail built by the AFK Group.
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