Abstract

Dawsonite (NaAl (OH) 2 CO 3 ) is relatively abundant (up to 25 percent) as a rock-forming constituent of a zone within the Green River oil shales in the Piceance Creek Basin, Colorado, and also occurs in Pleistocene ash beds, Olduvai Gorge, Tanzania. The mineral is most readily distinguished from other carbonates of the Green River Formation by optical properties and X-ray diffraction. 'In five of the seven known occurrences, the formation of dawsonite has been related to hydrothermal activity connected with volcanic episodes, with varying ore mineralization.' The Green River and Olduvai Gorge occurrences, however, are ascribed to reaction of carbonate solutions with nepheline of the original sediments.

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