Introduction
The Minnesota State Capitol’s gleaming white exterior — particularly its dome and upper façades — is clad in white Georgia marble, a metamorphic rock prized for its beauty and workability. This EarthCache lesson explores where that marble came from, how it formed, and what geological stories it tells.
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What Is Marble?
Marble is a metamorphic rock formed when limestone is subjected to heat and pressure deep within Earth’s crust. In this process:
• Calcite crystals in limestone recrystallize.
• The original sedimentary layering is destroyed.
• The result is a denser, interlocking mosaic of calcite grains — often white and fine-textured.
Marble reacts with weak acid (like vinegar) by fizzing due to its calcite content — Please do not attempt this field test at the Capitol! Acid rain tends to react with the calcite content of the marble as well.
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The Marble of the Capitol: Source & History
Source: The white marble used on the Capitol’s exterior was quarried in Pickens County, Georgia, primarily from the Amicalola quarry, a historic source known for its relatively pure, bright white stone.
Why Georgia Marble?
Architect Cass Gilbert specified Georgia marble for its brilliant color and classical look, believing that darker local stone would make the building appear “gloomy and forbidding.” At the time of construction (1896-1905), the Minnesota legislature debated the cost, but Gilbert insisted the lighter marble would reflect light better, making the Capitol appear monumental. Today, the Capitol is less brilliant than it was originally, mainly due to years of air pollution.
Transport & Construction:
Quarried blocks were shipped from Georgia north to St. Paul, where local craftspeople finished and installed them.
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Geologic Features You Can Observe
When you visit the Minnesota Capitol:
Color & Texture
• The marble is predominantly white or light gray with a medium to coarse crystalline texture.
• Look for subtle veining or mineral variations in the stone surface.
Weathering Effects
Marble weathers over time through:
• Freeze-thaw cycles, which can cause small cracks and surface roughening.
• Chemical weathering, as acidic rainwater slightly dissolves calcite.
These processes are why the Capitol has undergone restoration work on its marble façade in recent years. Replacement marble has been shipped in over the years from the same Georgia quarry that supplied the original stone to maintain consistency.
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Earth Science Significance
The Georgia marble of the Minnesota Capitol tells a powerful geologic story:
• Formed in ancient oceans
• Transformed during continental collision
• Transported over 1,000 miles
• Standing today in a northern climate vastly different from its origin
It is an excellent example of how tectonics, mineralogy, and human decision-making intersect in the building environment.
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EarthCache Visitor Tasks
To log this EarthCache, answer the following:
1. Marble Identification:
At the Capitol site, describe a visible patch of marble. What color and texture is it, and do you see any visible veins?
2. Weathering Notes:
Describe two signs of weathering on the marble surface you can observe (roughness, cracks, discoloration).
3. Geo-History Reflection:
Explain why the marble from Georgia — rather than local stone — was chosen for this building based on what you’ve read here.
4. Photo Requirement:
Post a photo of yourself, your group, or something that identifies you with the State Capitol Building in the background.