How is Vermont Marble formed?
Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite (CaCO3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite. Under the conditions of metamorphism, the calcite in the limestone recrystallizes to form a rock that is a mass of interlocking calcite crystals.
Most marble forms at convergent plate boundaries where large areas of Earth's crust are exposed to regional metamorphism. Some marble also forms by contact metamorphism when a hot magma body heats adjacent limestone or dolostone.
Before metamorphism, the calcite in the limestone is often in the form of lithified fossil material and biological debris. During metamorphism, this calcite recrystallizes and the texture of the rock changes. In the early stages of the limestone-to-marble transformation, the calcite crystals in the rock are very small. In a freshly-broken hand specimen, they might only be recognized as a sugary sparkle of light reflecting from their tiny cleavage faces when the rock is played in the light.
As metamorphism progresses, the crystals grow larger and become easily recognizable as interlocking crystals of calcite. Recrystallization obscures the original fossils and sedimentary structures of the limestone. It also occurs without forming foliation, which normally is found in rocks that are altered by the directed pressure of a convergent plate boundary.
Recrystallization is what marks the separation between limestone and marble. Marble that has been exposed to low levels of metamorphism will have very small calcite crystals. The crystals become larger as the level of metamorphism progresses. Clay minerals within the marble will alter to micas and more complex silicate structures as the level of metamorphism increases.
Marble is an exceedingly dense metamorphic rock, with Vermont Marble having an average density of 160 lbs/ft3.
Uses of Vermont Marble:
Vermont marble has a long and storied history. Marble is found on the western side of Vermont in places like Danby and Proctor. As far back as 1894, the Vermont Marble Company in Proctor had 1,800 workers. These workers removed the marble from local quarries. They shaped it into blocks and columns for buildings. They carved it to make statues and tombstones. Some of these workers were immigrants from Italy and Ireland.
There are prominent buildings and monuments made from Vermont marble all over the United States and the world including many significant Washington, D.C. structures including:
- Thomas Jefferson Memorial
- US Supreme Court Building
- Rayburn House Office Building
- Russell Senate Office Building
- Arlington Memorial Amphitheater
- Arlington National Cemetery
- Tomb of the Unknown Soldier – the marble sarcophagus came from the Vermont Marble company’s Colorado quarry but the carving was done in Proctor and the tomb base is Vermont marble
- National Gallery West Building - includes Vermont marble on the interior
- Union Station is constructed from Vermont granite with a Vermont marble base
- U.S. Capitol – West Elevation Balustrade
- Memorial Continental Hall - DAR Building (on the Ellipse, adjacent to the White House)
- District of Columbia War Memorial (WW I)
- Washington DC Municipal Building, 1350 Pennsylvania Ave.
- White House Remodeling, 1950’s
- Lincoln Memorial – Marble form the VMC’s Yule Colorado Quarry
- Arlington Memorial Bridge
- Smithsonian Museum of Natural History
- US Department of Agriculture, North Buildings
How to Claim this Cache:
In order to claim this cache you must answer the following questions about the pieces of Vermont Marble at the given coordinates. Send your answers to me via the message center. Feel free to log the find immediately after sending your answers. I will typically only respond if you have an incorrect answer or you have not provided enough information.
- Estimate the overall volume (length * width * height) of the piece of the large block of marble on your right (as you face away from the visitors center).
- Using the given density in this lesson, calculate the weight of the large marble block.
- Look closely at the marble. What color are the veins? What can you infer about the limestone that formed this marble.
- Optional: Take a photo of yourself at GZ and post it with your log.
Sources:
- The Vermont Marble Muesum - "A History of Vermont Marble"
- The Engineering Toolbox - "Densities of Solids"
- University of Vermont - "Unit 2: Vermont Geology and Landscapes"