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Formula: NaH(CO3)
Carbonate
Specific gravity: 2.21
Hardness: 2½
Streak: White
Colour: Colourless, white, grey, buff
Solubility: Readily soluble in water and glycerine
Environments
Nahcolite is naturally occurring sodium bicarbonate. It is found as a precipitate from hot springs, as
efflorescences around saline lakes and in brines, formed at a late stage in differentiated alkalic massifs, and as a
solid in liquid inclusions in a variety of other mineral species. Associated minerals include
trona, thermonatrite,
thénardite, halite,
gaylussite, burkeite,
northupite and borax
(HOM).
Localities
At the type locality, Mount Vesuvius, Metropolitan City of Naples, Campania, Italy, nahcolite has been found
in a lava tunnel associated with halite and
thénardite
(Mindat).
Nahcolite from Mount Vesuvius - Image
At Stufe di Nerone, Pozzuoli, Metropolitan City of Naples, Campania, Italy, in old Roman conduit, nahcolite
was found admixed with
trona and
thermonatrite as an efflorescence
(Dana).
At Little Mogadi Dry Lake, Kajiado County, Kenya, nahcolite occurs as fibrous
pseudomorphs
after gaylussite, and as alteration rims around
thermonatrite
(Dana).
At Searles Lake, San Bernardino County, California, USA, nahcolite occurs in thin beds associated with
gaylussite, thénardite,
burkeite, northupite,
borax and halite
(Dana).
Nahcolite from Searles Lake - Image
At Anvil Points, Rifle, Garfield County, Colorado, USA, a number of underground openings have penetrated the
high-grade oil-shale facies that contain the cavities, some of which
were unleached and contain nahcolite, in crystalline, cleavable masses in concretions as large as five feet
across and as small as a pea. It also was found in layers up to four inches thick intercalcated between
oil-shale beds. The nahcolite in the concretions varies in
colour from colourless, through white, yellow, brown and black. Most often the colour is a dirty brown because of the
bitumen dispersed throughout the mineral.
The nahcolite occurring in the layers is pure white, translucent, and occurs as fibrous crystals at right
angles to the bedding. It has a pearly opalescence and resembles the satin spar variety of
gypsum
(AM 32.117-120).
Nahcolite from Anvil Points - Image
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