Cemetery Series: Cemetery Geology

Cortland Rural Cemetery. Photo credit to PBM.

Cemeteries serve as memorials to our loved one’s lives and stories, but the stories of those who have passed on aren’t the only ones that can be found in a graveyard. Tales of geology, environmental health, and wildlife are also hidden there. Today I’m going to share some of the geological stories of headstones.

Kings Chapel Burying Ground. Photo by author.

Author's image.

Here are a few popular stones used in cemeteries over the centuries.

Granite

Granite. A creative commons image.

Granite is a durable igneous rock that makes for a long lasting tombstone. People began to use granite for cemetery monuments in the 1860s and it remains a popular stone for memorials to this day. Granite is formed from magma which cooled about ten miles below the earth’s surface. Whenever granite shows up at the surface of the earth that means the ten miles of earth covering it have eroded away over time leaving the granite visible. North Carolina is home to the world’s largest open-faced granite quarry. All stone there is mined directly from the surface. Granite comes in a variety of consistencies and colors determined by the composition of the minerals in the rock. Quartz, mica, and various feldspars make up most of granite and give it a characteristic speckled look. Sometimes granite contains xenoliths, sections of foreign rocks which did not melt and integrate into granite smoothly, but remained their own species of rock.

Granite holds up well under weathering, though the mica in it may degrade leaving it pitted. Stains from soot can darken granite, and lichens, moss, and ivy growing on the stone can change its appearance as well.

Quincy Granite Scandal

In the 19th century a dark variety of granite found near Boston known as Quincy granite was all the rage. Quincy granite got its dark color from some of its feldspars which were degrading into clay in a process called kaolinization. Quincy granite was used in many buildings and monuments until people found out that much of the stone being sold wasn’t actually Quincy granite at all, but a lighter granite rubbed with carbon and oil to make it darker. This dye eventually faded, leaving the stones splotchy and the customers disgruntled. After this scam no one wanted anything to do with Quincy granite.

Sandstone

Prepared sandstone sample. A public domain image.

While granite (non-dyed) holds up well under weathering, sandstone is probably the least durable rock used in cemeteries. Whole layers easily flake off as wind and rain wear down the stone. Monuments and headstones made from sandstone were popular from 1650-1890.

Monument at Cortland Rural Cemetery. Photo credit to PBM.

Sandstone is a sedimentary rock formed from sandy broken up pieces of other rocks deposited at the bottom of a river or sea. When these deposits were subjected to intense pressure, they condensed into a new rock, sandstone. The color of sandstone differs widely across sandstone species depending on where they formed and how they weathered. Sandstone is often striped with different colored sediment. In addition to miscellaneous rock pieces, sandstone often contains quartz and feldspar, and is held together by silica, calcite, or iron oxides.

Limestone

Limestone quarry. A creative commons image.

Limestone is similar to sandstone, but it holds up to weathering better and it is formed from calcite and silicate sediment, not sand. Impurities in the sediment will create darker limestone, but lighter varieties with fewer impurities are the most prized. The calcite and silicate either directly precipitate from the seawater or are obtained from the abandoned shells of sea creatures lying on the ocean floor. Some limestone contains fossils of these organisms. Limestone commonly forms in tropical or subtropical seas where calcite and silicate are abundant.

Monument at Cortland Rural Cemetery. Photo credit to PBM.

Most calcite and silicate sediments are compressed into limestone in the same way sand is compressed into sandstone. Some limestones even contain visible sedimentary layers like sandstone does. However, oolitic limestone, also used for headstones, forms in a different way and doesn’t contain these layers. Small grains of sand roll about the sea floor collecting calcite, which acts as a matrix to bind these grains together, and voilà, oolitic limestone is formed.

Ooids in a thin-section. A public domain image. 

Headstones made of limestone were most popular from 1780-1930, but limestone was used much earlier to make the first sarcophagi. Sarcophagus literally means “flesh eat,” a rather disturbing name which stems from the unusual limestone used to make sarcophagi which ate away at human flesh.

Sarcophagus of Pharaoh Merenptah. A creative commons image.

Marble

 Marble. A creative commons image.

After limestone is metamorphosized at high temperatures and pressures it becomes marble. The purest marble is perfectly white and has a sugary texture. Marble is highly sought after for its elegant beauty. Marble may be beautiful, but over time its glory fades as carbonization brought on by rainfall causes its surface to recede, rendering headstone inscriptions illegible. In an effort to combat the lost lettering, lead letters were attached with pins to marble monuments, but eventually surface recession caused these letters to fall out. Marble is also easily stained with lichens or soot.

Author's own image.

Marble was in vogue from 1780-1930. The world’s most prized marble has no impurities and comes from Carrara, Italy. Michelangelo used Carrara marble to carve his famous statue of David, and Leonardo Da Vinci helped a quarrying machine for this site. Today, the supply of Carrara marble is running low. Oddly enough, the world’s cheapest marble, Italian grey marble, also hails from Carrara.

Monument from Cortland Rural Cemetery. Photo credit to PBM.

The United States contains several marble sources on the east coast, the most popular sites are Barre, Vermont and Knoxville, Tennessee. The land which now forms Vermont and Tennessee was once the bottom of a tropical sea, which provided the right conditions for limestone formation. This limestone then metamorphosized into marble. 

Monument from Cortland Rural Cemetery. Photo credit to PBM.

Slate

Slate. A public domain image.

Slate, like marble, is sedimentary rock that was metamorphosized to become a new variety of stone. Unlike marble, slate is formed from sedimentary rock made of mud and possibly volcanic ash, not limestone. Slate tends to be dark grey or tinted deep purple or green from the volcanic ash. It is layered in thin sheets that peel apart easily. Gravestones made of slate are often coated with a protective material to prevent water from getting between the layers and pushing them apart. Once the coating is on, slate weathers well given its hard nature. Being hard isn’t always good for a gravestone, however, as it is highly difficult to carve inscriptions into slate. Still, professional gravestone carvers in the later 1600s and early 1700s made impressive carvings on slate of death imagery such as skulls, hourglasses and cherubs. Carved slate gravestones in New England are a crucial relics of Puritan art.

Carved slate gravestone from King's Chapel Burying Ground. Photo by author.

Carved slate gravestone from King's Chapel Burying Ground. Photo by author.

Judge Hathorne's grave. Salem, MA. Photo by author.

Modern Additions

Larvikite and Gabbro are the most common stones used to make grave markers.

Larvikite. A public domain image.

Larvikite is a coarse grained igneous rock with an abundance of feldspars, which give it an iridescent shine. Most larvikite is mined in Scandinavia. It is still unclear how larvikite will weather since most gravestones made of it haven’t been up very long.

Gabbro. A public domain image.

Gabbro is also an igneous rock that appears dark grey, but turns black with polish. Molten black and white feldspars form this rock, which weathers easily when exposed to water. Gabbro is often mistaken for, and even sold as, black granite. One beautiful variety of Gabbro, black galaxy, is flecked with bronzite which gives the stone the aura of a starry sky at night.

Gravestones and monuments help us to honor our loved ones and give cemeteries their characteristic beauty. But how do these stones and what’s underneath them impact the world around them? Stay tuned for the next installment of the Cemetery Series: Death and the Environment.

Monument at Cortland Rural Cemetery. Photo credit to PBM.

Note:
In this post I used the terms gravestone, headstone, grave marker and tombstone interchangeably. By common usage, all refer to some type of burial marker. However, gravestones, headstones, grave markers, and tombstones actually are specific terms which refer to different styles of burial markers. Here is a link to a page which explains the exact definition of these terms for those who are interested. 

Sources.