Roaming Rocks
By Marcia G Bjornerud
Metamorphic minerals are emissaries from the deep, traveling to distant realms and revealing the restless nature of Earth.
This Article From Issue
March-April 2025
Volume 113, Number 2
Page 90
As geological sites go, this one is easy to miss. It’s just a low rise of exposed rock along a back road in northern Wisconsin, outside a town whose one claim to fame is a tavern that the gangster John Dillinger used as a hideout in the 1930s. Even though I’ve been to this outcrop many times before, I drive right past it on this autumn day and need to look for a place where it’s possible for three university vans to turn around. We manage to make the maneuver, come back from the other direction, and park on the shoulder. Students spill out of the vehicles, clearly underwhelmed, puzzled at why we’ve bothered to stop here. They don’t yet realize that this place is a secret portal into Earth’s interior.
QUICK TAKE
- Metamorphic rocks traveled from Earth’s surface to its mantle and back out again. Along the way, they collected evidence of the planet’s past and of its inaccessible interior.
- For rocks to become metamorphic, they require heat, pressure, and water. Studying the types of minerals in a location can reveal the area’s environment millions of years ago.
- Plate tectonics moves rocks through the Earth, and they recrystallize in their new environments. Metamorphic rocks are abundant on Earth but are rare in the Solar System.
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