Rising above the Saint John River, the New Brunswick Legislative Building is crowned with a striking green roof. While it may look decorative today, this colour is the result of an important geological and chemical process that links the building to Earth’s natural systems.
This EarthCache explores how copper, a naturally occurring element mined from the Earth, changes over time when exposed to air, water, and the environment.
What Is Copper?
Copper is a native element, meaning it can occur naturally in pure form within the Earth’s crust. It is valued for its durability, malleability, and resistance to corrosion—qualities that make it ideal for roofing.
In New Brunswick, copper is commonly associated with volcanic massive sulfide (VMS) deposits, such as those found in the Bathurst Mining Camp. These deposits form when hot, mineral-rich fluids rise through volcanic rock and cool, leaving metal-rich ores behind.
From Shiny Metal to Green Patina
When freshly installed, copper has a reddish-brown metallic colour. Over time, exposure to the atmosphere causes chemical weathering:
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Oxidation – Copper reacts with oxygen, forming darker copper oxides.
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Reaction with moisture and carbon dioxide – These oxides further react to form copper carbonate compounds.
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Patina formation – The familiar green coating develops.
This green layer, called a patina, actually protects the copper beneath it, slowing further corrosion. Unlike rust on iron, this weathering process helps preserve the material rather than destroy it.
Why This Site Is Special
This roof provides an excellent urban example of chemical weathering, allowing visitors to observe geological processes without leaving the city. It also connects the natural geology of New Brunswick to how Earth materials are used in human construction.
What to Look For
From the public grounds, observe the copper roof:
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Note the colour and texture
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Look for variations in shade
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Consider how exposure to rain, sunlight, and air affects the surface
No touching or entering the building is required.
To log this earthcache, go to the posted coordinates, take a photo of yourself or a personal item at New Brunswick Legislature to post in your log, and complete the following tasks and send your answers in a private message to the cache owner.
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Observation
Describe the dominant colour of the copper roof today. What does this colour indicate about the stage of weathering the copper is in?
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Comparison
Do you notice areas of the roof that appear lighter or darker green? Suggest one environmental factor that could cause these differences.
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Geoscience Interpretation
Is the change in colour of the copper roof an example of physical or chemical weathering? Explain your answer using what you observe.
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Geology Connection
Copper must be mined from rock before it can be used in buildings. Name one type of geological environment where copper is commonly found and briefly describe how copper moves from rock to roof.
Optional: Feel free to include a photo of yourself or your GPS with the building in the background (not required for logging).
Accessibility & Safety
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Accessible year-round from public walkways
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No climbing, touching, or entering the building
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Please respect the grounds and other visitors