Feb 6, 2024 - News

How Castle Rock in Colorado stands the test of time

Castle Rock. Photo courtesy of Jeff Albright

Castle Rock. Photo: Courtesy of Jeff Albright

Castle Rock is a Colorado gem. And now we know it's an actual gem, too.

What to know: The butte is made of opal — the same stone often used in jewelry — that makes it resistant to erosion.

  • The finding is the secret to why Castle Rock looms tall over the town of the same name and why other land formations erode, according to a new research paper from scientists at the Denver Museum of Nature and Science.
  • The particles of sand in the castle-shaped butte and nearby Castlewood Canyon State Park are encased in opal, which makes it harder than most concrete, the researchers found.
Mark Longman holding a sliced-open sample of opal-cemented sandstone from Castlewood Canyon State Park. Photo courtesy of Joan Burleson
Mark Longman holding a sliced-open sample of opal-cemented sandstone from Castlewood Canyon State Park. Photo: Courtesy of Joan Burleson

What they're saying: "Generally, exposed sedimentary rocks in these areas would be prone to erosion and might crumble into rubble," James Hagadorn, the museum's geology curator, said in a statement.

  • "The key to Castle Rock's exceptional durability, it turns out, is that it's held together by a unique and captivating gem mineral, opal."
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