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Nahcolite from California (size: 9.5 x 8 x 4 cm)
CategoryCarbonate mineral
(repeating unit)
Sodium bicarbonate (NaHCO3)
IMA symbolNah[1]
Strunz classification5.AA.15
Dana classification13.01.01.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/n
Unit cella = 7.47, b = 9.68
c = 3.48 [Å]; β = 93.38°; Z = 4
ColourWhite to colourless, may be grey to brown
Crystal habitElongated crystals, fibrous masses, friable porous aggregates
TwinningCommon on [101]
Cleavage{101} perfect, {111} good, {100} distinct
Mohs scale hardness2.5
LustreVitreous - resinous
DiaphaneityTransparent to translucent
Specific gravity2.21
Optical propertiesBiaxial (-)
Refractive indexnα = 1.377 nβ = 1.503 nγ = 1.583
Birefringenceδ = 0.206
Ultraviolet fluorescenceShort UV=blue-white cream-yellow, Long UV=cream-yellow
SolubilitySoluble in water

Nahcolite is a soft, colourless or white carbonate mineral with the composition of sodium bicarbonate (NaHCO3) also called thermokalite. It crystallizes in the monoclinic system.[4]

Nahcolite was first described in 1928 for an occurrence in a lava tunnel at Mount Vesuvius, Italy.[2] Its name refers to the elements which compose it: Na, H, C, and O.[5] It occurs as a hot spring and saline lake precipitate or efflorescence; in differentiated alkalic massifs; in fluid inclusions as a daughter mineral phase and in evaporite deposits.[2][4]

It occurs in association with trona, thermonatrite, thenardite, halite, gaylussite, burkeite, northupite and borax.[3] It has been reported in a Roman conduit at Stufe de Nerone, Campi Flegrei, near Naples; in the U. S. from Searles Lake, San Bernardino County, California; in the Green River Formation, Colorado and Utah; in the Tincalayu deposit, Salar del Hombre Muerto, Salta Province, Argentina; on Mt. Alluaiv, Lovozero Massif and Khibiny Massif, Kola Peninsula, Russia; and around Mount Erebus, Victoria Land, Antarctica.[3]

Nahcolite deposition model


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85: 291–320.
  2. ^ a b c Nahcolite on
  3. ^ a b c Nahcolite in the Handbook of Mineralogy
  4. ^ a b c Nahcolite data on Webmineral
  5. ^ Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig: Dana's new mineralogy, John Wiley & Sons, 1997