A Grave Subject
The focus of this Earthcache is the geology of gravestones used in the 1700s in New England. Availability of the minerals used is key.
The geology of New England played an important role in determining where gravestone carvers would work, and the types of material that they used. Most gravestones of this period were made in either slate, schist, sandstone, or marble, depending on what was locally available.
Here you will see a map that shows the bedrock geology of the region, specifically the areas that have one of those four types of bedrock. This map strongly correlates to the distribution of 1700s gravestones, with slate in the Boston area, schist in eastern Connecticut and west-central Massachusetts, sandstone in the Connecticut River Valley, and marble in the Berkshires and western Vermont. Also included are photos of gravestones from each of these different types of bedrock.
The white areas on the map are generally gneiss, granite, and other types of metamorphic stone that weren’t typically used for gravestones in the 1700s.
Sandstone is formed through the compaction and cementation of sand-sized grains, primarily composed of quartz and feldspar, over a great many years. This process occurs when sediments are deposited in environments like rivers, seas, or deserts, and then compacted under pressure, with minerals filling the gaps between the grains to bind them together. Brownstone is a type of sandstone as is quartzite. Sandstone is converted into quartzite through heating and pressure. The term quartzite is also sometimes used for very hard but unmetamorphosed sandstones that are composed of quartz grains thoroughly cemented with additional quartz.
Sandstone has a hardness rating of 6 to 7 on the Mohs hardness scale, indicating it is relatively hard and durable compared to many other natural stones.
Slate is formed from the metamorphism of shale or mudstone, which are sedimentary rocks composed mainly of clay or volcanic ash. This process occurs under low-grade conditions of heat and pressure, resulting in a fine-grained, foliated rock. Slate has a hardness rating of 2.5 to 4 on the Mohs scale, making it softer than granite and quartz but harder than limestone and marble.
Schist is Slate is formed from the metamorphism of shale or mudstone, which are sedimentary rocks composed mainly of clay or volcanic ash. This process occurs under low-grade conditions of heat and pressure, resulting in a fine-grained, foliated rock. Slate has a hardness rating of 2.5 to 4 on the Mohs scale, making it softer than granite and quartz but harder than limestone and marble.
of metamorphism, where fine-grained sedimentary rocks like shale are subjected to moderate heat and pressure, causing the clay minerals to transform into platy minerals such as mica. Schist has a hardness rating of approximately 3.5 to 4 on the Mohs hardness scale, indicating it is a medium-hard rock that can be scratched by harder materials. This hardness is due to its composition, which often includes platy minerals like mica.
Marble is formed when limestone or dolomite undergoes intense heat and pressure, causing the minerals to recrystallize in a process called metamorphism. This results in a denser rock with a distinctive crystalline structure. Marble has a hardness of about 3 on the Mohs scale, making it relatively soft compared to other stones.
Brownstone is a type of sandstone as is quartzite. Sandstone is converted into quartzite through heating and pressure. The term quartzite is also sometimes used for very hard but unmetamorphosed sandstones that are composed of quartz grains thoroughly cemented with additional quartz.
Soapstone wasn’t used for gravestones on a large scale like the other 4 types because it does not hold up to the elements as well. Also, limestone is soft marble and was rarely used for gravestones.
Although prevalent today, granite didn’t become usable for gravestones until modern machinery was developed in the late 1800's.
At the given coordinates you will find a gravestone* which was most likely sourced from the Pin Hill Quarry in Harvard.
To receive credit for this Earthcache answer the following questions.
What type of stone is at ground zero?
To the left are 4 stones in a row. Are they the same mineral composition as the first one? If not, what type of stone is it?
There are 2 nearby taller obelisk monuments. What type of stone are each of these made of? Does this tell you anything about those stones?
Post a photo of yourself near a (likely) locally mined stone. (You need not include your face of you are camera shy)
Data source:
Research done by Derek Strahan of Gravestones of New England,
U.S. Geological Survey, Generalized Lithology and Lithogeochemical Character of Near-Surface Bedrock in the New England Region
*This stone was carved by the grandson of the deceased. James Wilder (the carver) created many monuments in this area. He lived here in Lancaster.
Congratulations for Co FTF go to gpscouts, DaleW2001 and CavyGirl 🙂