What makes an Ellensburg blue, blue? And why is it so different from other blue agates around the world?
The answer is Teanaway basalt, according to Nick Zentner, Central Washington University geological sciences professor. Zentner, who is unabashedly enthusiastic about Washington geology—he hosts Central Rocks on KCWU-TV—says the mysterious blue stone was millions of years in the making and the result of massive geological forces that formed the Kittitas Valley.
As the Teanaway basalt—a 47 million year old rock formed from lava flows—cooled, large cavities within it were formed, allowing water to flow through it. This water left unique mineral deposits in the cavities and as these mineral deposits gradually hardened, they formed the treasured agate known as the Ellensburg blue.
"There are huge quantities throughout the Green Canyon area,” said Zentner, adding that most are still buried deep within the surrounding terrain. “They come to the surface with flowing water or with frost heave—it just takes a little looking."
And what makes the blue?
“It’s actually kind of an optical illusion, like why the sky is blue,” said Zentner. “A few years ago, a professor from New Zealand did all sorts of tests—mineral, chemical, X-ray diffraction studies—you name it—and discovered that the blue was the result of light hitting and refracting on very, very small micro-structures suspended in the quartz.”
Zentner also explained why the Ellensburg blue is different from other blue agates found round the world. “It is the uniformity of the blue color throughout the individual stone that is unique. Ellensburg blues can be anywhere from a very light ‘baby’ blue to a deep purplish blue—all of them prized by collectors.”
Zentner’s lecture on Ellensburg blues can be viewed on YouTube at http://www.youtube.com/watch?v=j8BFvKoabJ0&feature=youtu.be
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