Nebraska Symbols, Gem: Blue Agate

Blue Agate has been found in place in wind-deposited claystones in the Chadron Formation of Oligocene Age 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 is found in many deposit forms. Stalactite growths of the mineral are seen in numerous places and often assume fantastic shapes and forms. Chalcedony also may replace materials such as wood. The blue agate can be found in northwestern Nebraska. 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.

On 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 (Nebraska's Centennial).