CASTLE ROCK, Colo. — A new study is revealing more about the rock known as Castle Rock.
According to a study from the Denver Museum of Nature and Science, the rock formation's unique prominence and durability can partially be attributed to the presence of opal -- a gem that makes the rock face extremely resistant to erosion. You can also find it in many different types of jewelry.
“Like a rind on an orange, every sand grain and pebble in these rocks is encased in opal, which cements these particles together to make the rock harder than most concrete,” said Dr. James Hagadorn, the Tim & Kathryn Ryan Curator of Geology at the Denver Museum of Nature & Science.
Opal is amorphous, meaning it does not have a defined crystalline shape. Due to that fact, it's classified as not truly a mineral, but a mineraloid. It can be found throughout the world, including in Brazil, Mexico, Honduras and the western USA. Australia produces about 95% of the world's precious opal, and it's designated as that country's national gemstone.
The prominent butte, right in the city center of Castle Rock, is a popular spot for those looking to take a short hike.
According to the study, opal can also be found in rock structures in the nearby Castlewood Canyon State Park.
The paper, written by Dr. Mark Longman, Joan Burleson, and Hagadorn, can be found in the January edition of The Mountain Geologist.
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