nahkolit

Nahcolite, also spelled nahkolit in some sources, is the natural mineral form of sodium bicarbonate, NaHCO3. It is an evaporite mineral that forms in arid, alkaline lake environments where saline waters evaporate and concentrate bicarbonate ions. Nahcolite commonly occurs with other evaporite minerals such as trona (sodium carbonate) and halite and is known from several lacustrine basins, most notably the Green River Formation in the western United States.

Crystal habitat and properties: Nahcolite typically appears as colorless to white crystals or as earthy, white nodules. Well-formed specimens are transparent to translucent, with a vitreous to pearly luster. It has a soft Mohs hardness of about 2.5 and a density around 2.16 g/cm3. It is soluble in water and effervesces when treated with acids, a characteristic of bicarbonates. Crystal habit is often not well developed, with the mineral more commonly found as crusts, scales, or nodular masses.

Geologic and economic context: As the natural form of sodium bicarbonate, nahcolite has historical significance as a source of soda ash and baking soda. Today, most commercial sodium bicarbonate is produced synthetically, but nahcolite deposits in evaporite basins are mined where present. The Green River and other lacustrine basins represent the best-known examples of natural nahcolite occurrences.

See also: Trona, Natron, Sodium bicarbonate.