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Nahcolite from California (size: 9.5 x 8 x 4 cm)
Category Carbonate mineral
(repeating unit)
Sodium bicarbonate (NaHCO3)
Strunz classification 5.AA.15
Dana classification
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/n
Unit cell a = 7.47, b = 9.68
c = 3.48 [Å]; β = 93.38°; Z = 4
Colour White to colourless, may be grey to brown
Crystal habit Elongated crystals, fibrous masses, friable porous aggregates
Twinning Common on [101]
Cleavage {101} perfect, {111} good, {100} distinct
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 2.5
Lustre Vitreous - resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.21
Optical properties Biaxial (-)
Refractive index nα = 1.377 nβ = 1.503 nγ = 1.583
Birefringence δ = 0.206
Ultraviolet fluorescence Short UV=blue-white cream-yellow, Long UV=cream-yellow
Solubility Soluble in water
References [1][2][3]
Nahcolite deposition model

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.[3]

Nahcolite was first described in 1928 for an occurrence in a lava tunnel at Mount Vesuvius, Italy.[1] Its name refers to the elements which compose it: Na, H, C, and O.[4] 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.[1][3]

It occurs in association with trona, thermonatrite, thenardite, halite, gaylussite, burkeite, northupite and borax.[2] 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.[2]


  1. ^ a b c Nahcolite on
  2. ^ a b c Nahcolite in the Handbook of Mineralogy
  3. ^ a b c Nahcolite data on Webmineral
  4. ^ Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig: Dana's new mineralogy, John Wiley & Sons, 1997