During Nebraska's centennial, the governor signed a bill designating blue Chalcedony, commonly called the blue Agate, as Nebraska's official state gemstone. The Blue Agate became the state gem on March 1, 1967 .
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The specific named Blue Agate has been found in place in wind-deposited claystones in the Chadron Formation of Oligocene Age in northwestern Nebraska in Sioux and Dawes counties. These gems have been found in colors other than blue and the large oval stone is a doublet with a blackened back to highlight the plumes in this material. Chalcedony, the more correct name, is found in many deposit forms. Stalactite growths of the mineral are seen in numerous places and often assume fantastic shapes and forms. It also may replace materials such as wood. The Chalcedony probably originated from silica that was freed when devitrification (changing from a glassy to a crystalline state) of wind-blown volcanic ash took place. The Chalcedony appears to have formed in or near sources of alkaline water and is also known by the name 'ledge Agate".
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As a side note, do not confuse Ellensburg Blue Agate with Nebraska Blue Agate. "Ellensburg Blue" agate is found as an amygdaloidal agate nodule or geode in Kittitas County near Ellensburg, Washington. Colors grade from almost white to a rich, deep, pure blue.
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Although Nebraska's blue Agate (Chalcedony) makes nice specimens and lapidary slabs, it does not normally produce crystals for faceting. Even obtaining a piece large enough for a clear cabachon is unusual.
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