This earthcache will examine the different types of weathering effects on headstones and how the type of stone used for the headstones can influence erosion. Take note that this earthcache is rated with a high difficulty level and it will take some time to gather the necessary informatin in order to complete. You will need to learn about the materials used in constructing these grave markers, in addition to the different types of weathering that has affected them. You will be required to visit several sites within the Richmond Cemetery as well as read what is included on the cache page. This is rated as a 2.5 terrain earthcache because of uneven terrain with hills and ground that can be slick and marked with holes and depressions.
The posted cordinates will bring you to the Main Street gate of the Richmond Cemetery (hours are 8 a.m. to 4:00 p.m. daily. The hours of the Summit Street gate are 8:00 a.m. to 5:00 p.m. from November 1st to March 31st and from 8:00 a.m. to 7:00 p.m. April 1st to October 31st). Please be respectful of the area and obey all cemetery rules.
The Richmond Cemetery spans 56 acres in size and is the largest cemetery in the area. It is located near downtown Richmond and was chartered in 1848 and later established in 1856.
Geologic Composition of Gravestones
Gravestones are made of many different types of rocks, ranging from metamorphic rocks like marble and slate, to plutonic rocks like granite and diabase, to sedimentary rocks like sandstone and limestone. The selection of gravestones is often dependent on aesthetic values and practical use.
Granite is the most common material used for gravestones today. It gained popularity at the end of the 19th century due to its durability to erosional forces such as weather. It is a light-colored igneous rock that was at one time liquid below the earth’s surface that cooled over time. Granite rock is distinguished by large grains that can be seen with the human eye. It is composed mainly of quartz, feldspar, and other interlocking materials such as biotite. Small amounts of mica or other types of minterals give with granite different colors, such as red, pink, gray, or white color with dark mineral grains visible throughout the rock. Polished granite surfaces have lasted over 100 years without showing any major signs of deterioration from weathering.
Marble was a very common headstone material through the 19th century. It is a metamorphic rock containing carbonate minerals created after limestone undergoes metamorphism (rocks subjected to heat and pressure over time, usually while buried deep below earth's surface). Marble is composed primarily of the mineral calcite, but in its less pure states also contains other minerals, such as clay, micas, quartz, pyrite, iron oxides, and graphite. In its most pure form marble is white with less pure forms containing ribbons of other colors. Pure white marble shines when polished, but after a decade after exposed to different types of weathering, becomes pitted and stained. If you touch weathered marble, fine grains will brush off the surface. It is highly susceptible to acid rain and other chemical weathering due to its high calcium carbonate content. It can also be damaged if set into or repaired by cement because cement traps water inside the material and causes easy breakage of the stone.
Limestone is a sedimentary rock that contains a high calcium carbonate content due to skeletal fragments of marine organisms such as corals and shells that once lived in shallow marine water, as well as containing silica, sand, silt, and clay that built up over time. Marble is created from limestone that has been metamorphosized (subjected to extreme heat and pressure below the earth’s surface over time). Limestone was used for headstones in the 1800s because it was readily available in many areas and can be engraved rather easily like sandstone. Limestone is a darker color than marble and tends to appear gray.
Sandstone is a sedimentary rock which is composed of fine sand grains which have been compressed together to form a solid rock. Sandstone is fairly porous and while the grains themselves might be hard, the material between them is softer and prone to erode away faster. Gravestones made from sandstone are easier to carve, but because of their poor defense against weathering, they erode quicker than other stones. The erosion occurs when moisture gets trapped between the layers of sandstone and when it freezes and expands, the layers flake off or blister the surface of the stone. They can also exhibit a discoloration to the surface of the stone due to a reaction with sulfur dioxide in the air or have lichen growth that use the calcium carbonate in the sandstone as a food source.
Slate is a very fine-grained foliated metamorphic rock. It is very durable and inscriptions made in slate last for long periods of time. Slade is, however, susceptible to lamination, which causes a break in the layers of the rock and often results in a total break of the stone itself.
Concrete is also a medium that is used for monuments in cemeteries. Concrete is a composite material composed of fine and coarse aggregate (including sand, gravel, crushed stone, slag) bonded together with a fluid cement (cement paste) that hardens over time. Most concretes use lime (calcium oxide or calcium hydroxide) as their cement/bonding agent. Depending on the cemetery, concrete monuments may be used as decoration around other headstones, or they could be used as a headstone themselves. Common concrete monuments are angels, crosses or urns. They are very economical and easy to make.
Weathering
Weathering is the altering of the physical and/or chemical composition of earth materials due to the action of weather conditions. This can include changes to color, texture, composition, or other forms to exposed objects. Headstones are subjected to weathering just by being placed in a cemetery. Headstones provide a useful means of observing and measuring the weathering of different types of rock over relatively long and easily measurable periods of time. Below are types and characteristics of weathering forms.
Black crusts - Black deposits often found in sheltered areas. On marble headstones these crusts often resemble cauliflower on close-up examination, which is characteristic of calcium sulfate, a crust formed by dry deposition. Where crusts form on exposed areas these are likely to be deposits of soot and particulate matter.
Blistering - A domed or raised surface to the headstone appears and makes a hollow sound when tapped. Over time the dome bursts and flakes of stone fall away from the dome. The inside of the blister may appear to be composed of more friable material.
Contour weathering - This occurs when an entire surface breaks away from the headstone as a single sheet. Often the sheet tends to follow the contours of the underlying carved form.
Flaking - Fragments of varying sizes become detached from surface and may dislodge from the main body of a sheet of detaching material or to the underlying mass of the gravestone.
Granular disintegration - Mineral grains are visible as protruding forms on the surface and has a grainy feel when touched. There is very little or no flaking. The edges of the lettering may become rounded and less distinct as weathering proceeds towards the edges of the gravestone.
Organic forms - Often there are algae growths or lichen on the headstone surface, which indicate the regular presence of moisture on a surface. Under very moist conditions, moss can be found on old headstones.
Pitting - Depressions that form on the surface of a headstone that are either shallow or deep.
Types of Weathering
Weathering is defined as breaking down rock which stays in one place. It is often confused with the term erosion, which is rock that has been transported and worn down. There are three basic types of weathering - Physical, Chemical, and Biological.
Physical weathering has two types: expansion-contraction weathering and freeze-thaw weathering. Expansion-contraction weathering is caused by heating of the rock by the sun. During high daytime temperatures, the outer rock expands and then cools rapidly at night. This causes stress in the rock surface, which then causes cracks to form. Freeze-thaw weathering is dependent on the expansion of water when it freezes into ice. When water is present in pore spaces, joints or cracks in rocks, it will expand when it freezes and push rocks apart, breaking them.
Chemical weathering occurs when chemical reactions occur on the surface of a rock, causing the minerals in the rock to decompose. Dissolution is a type of chemical weathering that plays a major role in the weathering of gravestones. Calcite is a carbonate mineral found in many gravestones. When it reacts with any acid, including the weak rainfall acids, it dissolves and over time, can slowly weather away gravestone markers. It particularly affects limestone, chalk and marble rocks at fast rates. Oxidation is another type of chemical weathering that occurs when oxygen combines with other substances and creates compounds called oxides that are often reddish or orange in color.
Biological weathering occurs when lichens and mosses attach themselves to the rock surfaces in order to take moisture and nutrients from the air, as well as from the rocks. They often occur as crusts on gravestones. The roots of the plants can also penetrate within the small spaces of the gravestones and cause bedding planes to separate. These plants can also secrete acids that promote the chemical breakdown of minerals in the stones. Tree or shrub roots can also push sections of gravestones apart and can cause them to fall to the ground.
Logging Requirements
To earn credit for this earthcache, please send the answers to the questions below for each waypoint to the CO in a timely manner. You will have six (6) sets of answers for the six (6) waypoints. In addition, please post a photo of yourself in the cemetery (face not required), but not at one of the gravestones listed for the waypoints that will give away any answers required for completion of this earthcache. Please do not include answers in your log.
- Describe the shape of the grave marker.
- What type of material was used for this headstone?
- Describe why you believe it is that type of material.
- What condition is the material in?
- What type of indicators of weathering do you see, if any?
- Explain what type of weathering (physical, chemical, biological) is happening here and if there more than one form present.
- What is the oldest recognizable date found on this monument?
Finally, after examing all of the gravestones at the six (6) waypoints, is there any specific type of stone that you believe holds up best over time to the various types of erosion? Explain why you think this is so. Do you believe that the shape of the monument has an affect on the rate of erosion? If yes, please describe how.
Sources:
https://www.gravestonepreservation.info/articles/stone-identification
https://www.nps.gov/tps/how-to-preserve/preservedocs/preservation-briefs/48Preserve-Brief-GraveMarkers.pdf
https://spadeandthegrave.com/2019/05/05/the-geologic-composition-weathering-of-gravestones/
https://www.livescience.com/18681-cemetery-gravestones-weathering-acid-rain.html
https://www.wyorksgeologytrust.org/misc/Teaching%20weathering%20in%20West%20Yorkshire.pdf