Nahcolite
Nahcolite from California (size: 9.5 x 8 x 4 cm)
General
Category	Carbonate mineral
Formula (repeating unit)	Sodium bicarbonate (NaHCO3)
IMA symbol	Nah[1]
Strunz classification	5.AA.15
Dana classification	13.01.01.01
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 ; β = 93.38°; Z = 4
Identification
Colour	White to colourless, may be grey to brown
Crystal habit	Elongated crystals, fibrous masses, friable porous aggregates
Twinning	Common on
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	[2][3][4]

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]

References