WEATHERING
Weathering is defined as the breakdown of rock, that is without being moved. Weathering processes depend upon the presence of water, the temperature, the mineral composition of the rock and its chemical composition.
WHY HERE?
Headstones are subjected to weathering simply by standing 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. The markers in this cemetery contain all three types of rocks: Sedimentary (sandstone), Igneous (granite) and Metamorphic (marble) making it valuable for comparison of headstone weathering.
The posted coordinates will bring you to two specific headstones. The one on the left (Holmes) is granite. The one on the right (Wortman) is marble. Both of these headstones were originally carved and placed here at about the same time, Holmes-1908 and Wortman-1909. This will allow us to compare the difference in the alteration of weathering based on the material. In addition, they both had additional carvings at a later date, Holmes-1937 and Wortman-1954. This will allow us to compare the difference in the alteration over time.
WEATHERING FACTORS
The weathering on headstones is a product of four interconnected factors.
The four factors are:
Material the headstone is made from
Environment the headstone is in
Form of the weathering on the headstone
Process by which the headstone is weathered
THE MOHS SCALE OF HARDNESS
The Mohs scale of mineral hardness is a qualitative ordinal scale that characterizes the scratch resistance of different minerals through the ability of a harder material to scratch a softer material. It was created by the German geologist and mineralogist Friedrich Mohs in 1812 and is one of several material science definitions of hardness, some of which are more quantitative.
GRANITE
Granite is a very hard stone and resistant to damage. Though the composition of various granite colors and varieties will vary from slab to slab, granite is generally is made up of a quartz, feldspar and an assorted variety of minerals, evoking a gritty look. Granite has a Mohs hardness rating of seven.
MARBLE
Marble is limestone that has been compacted and heated over millions of years. As a result, marble is less porous and slightly stronger than limestone. Depending on the limestone and the mineral combination within the marble, most marble rates from three to five on the Mohs hardness scale.
LETTERING ALTERATION
Rahn (1971) and Meierding (1993) suggested that the alteration of carved lettering on headstones follows a sequence of deterioration. The lettering becomes progressively roughened and difficult to read. The edges of the carved surface at first become less distinct as granular disintegration occurs. The whole letter begins to merge into the surface of the headstone as the agents of erosion remove the surface. Eventually the lettering becomes almost indistinguishable from the surface of the headstone itself. Once the lettering is indistinguishable the method become inappropriate to use. Although this method can not provide any absolute measurements of the amount of material lost, it can provide a relative measure of deterioration.
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Visual Weathering Class
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Visual Indicators of Class |
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1
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Lettering sharp and distinct. No evidence of change. |
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2
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Lettering slightly rounded showing evidence of some removal of grains. Still legible and cleat though. |
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3
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Lettering rounded. Edges clearly being removed and some original edges removed completely. Still legible and clear. |
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4
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Lettering rounded. All or most original edges removed, but lettering still legible, but increasingly becoming indistinct from the surface of gravestone. |
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5
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Lettering disintegrating. Lettering still just about legible, but now almost indistinguishable from the surface of the gravestone. |
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6
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What lettering? Lettering virtually disappeared. Need to be able to make out date to be able to date period over which lettering has disappeared. |
LOGGING REQUIREMENTS
In order to log this EarthCache, send me your answers to the following questions either through email or messaging from my profile page.
1: Determine the Visual Weathering Class for all four carvings:
1.h1: Holmes 1908
1.h2: Holmes 1937
1.w1: Wortman 1909
1.w2: Wortman 1954
2: Compare Holmes 1908 to Wortman 1909. These were carved near the same time and have been exposed to the same environment conditions for over 100 years. Which one has weathered more? Why?
3: Compare Holmes 1908 to Holmes 1937. How much more has the original carving weathered?
4: Compare Wortman 1909 to Wortman 1954. How much more has the original carving weathered?
* Pictures are not required but are appreciated. Please post a pic of you or your GPS with anything you find interesting around the cemetery.
REFERENCES
http://www.geologypage.com
https://www.granitemarblewa.com/