Trona from the Eocene of Wyoming, USA. (~10.7 centimeters across along the base)

The Green River Formation of Utah-Colorado-Wyoming is a widespread, Eocene-aged lake deposit. It is famous for having vast oil shale deposits and containing exquisitely-preserved fossils. The Green River also contains the world's largest sodium carbonate evaporite deposit, in the form of thick trona beds.

Trona is a scarce hydrous sodium bicarbonate-carbonate mineral - Na3(HCO3)(CO3)·2H2O. It is an evaporite mineral, formed by the evaporation of water and the precipitation of dissolved minerals. Most evaporites form when restricted ocean basins dry out, leaving behind rock salt, rock anhydrite, and rock gypsum. Trona is a nonmarine evaporite mineral. This specimen is from a trona horizon formed when water in ancient Lake Gosiute evaporated. The lake existed during the Early Eocene in southwestern Wyoming. As climate cycled from non-arid to arid, the lake's water levels waxed and waned. During times of significantly dry climate, the lake shrunk in size, became highly saline and highly alkaline, and dried out, resulting in alkaline evaporite deposits.

Green River trona beds have economic significance and are mined at several sites in Wyoming. The trona is processed and made into "soda ash", which has multiple uses in society.

Stratigraphy: thin trona bed (encountered in shaft sinking) above an actively mined trona horizon, Wilkins Peak Member, Green River Formation, Lower Eocene, ~49.9 to 51.5 Ma

Locality: Texasgulf's Blacks Fork Trona Mine, northeast of the town of Granger, western Sweetwater County, southwestern Wyoming, USA (vicinity of 41° 40' 22.60" North latitude, 109° 53' 55.10" West longitude)

See info. at: <a href="https://en.wikipedia.org/wiki/Green_River_Formation" rel="noreferrer nofollow">en.wikipedia.org/wiki/Green_River_Formation</a> and <a href="https://en.wikipedia.org/wiki/Sodium_carbonate" rel="noreferrer nofollow">en.wikipedia.org/wiki/Sodium_carbonate</a> and