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Formula: NaAl(SO4)2.6H2O
Hydrated normal sulphate
Crystal System: Monoclinic
Specific gravity: 2.06 measured, 2.066 calculated
Hardness: 3
Streak: White
Colour: Colourless; colourless in transmitted light
Solubility: Soluble in water
Environments
Evaporite deposits
Cave deposits
Tamarugite occurs under arid conditions by the oxidation of sulphides in aluminous and alkali-rich environments.
Common associates include alum-(K),
alunogen, anhydrite,
coquimbite, epsomite,
gypsum, halite,
halotrichite, mendozite,
meta-alunogen, pickeringite,
quenstedtite and
sideronatrite
(Mindat).
Localities
The type locality is Cerros Pintados, Tamarugal Province, Tarapacá, Chile.
At Faraglione Nico, Faraglioni di Levante, Porto Levante, Vulcano Island, Lipari, Eolie Islands, Messina Province,
Sicily, Italy, tamarugite was found on the eastern internal wall of the crater of Vulcanello, forming
incrustations on the walls and ceilings of cavities in basanitic
pyroclastic rocks. The cavities are due to erosion as well as to human activities.
Tamarugite occurs as white, porous aggregates of very thin, fragile, lamellar crystals with maximum dimensions of
less than 500 microns. A sample of several grams, with a tamarugite content of more than 85%, was collected.
Field evidence suggests that this tamarugite is of
supergene origin
(CM 19.403-407).
At the Diana Cave, Cerna valley, Caraş-Severin, Romania, an exceptional occurrence of tamarugite has been found
in a short karst cavity. It was formed by corrosion of the bedrock
(limestone and marls) by
a (SO4)2−-rich steam condensate resulting from oxidised S2− ions escaping from the
thermo-mineral water emerging from depth in the cave. Tamarugite forms dull white earthy aggregates of tabular
subhedral crystals never exceeding 15 μm across.
Marine evaporites are confirmed as the source of sulphur. The sulphate-acid
alteration of limestone with the contribution of Al3+ and
Na+ from the marls and the thermal water is responsible for the
formation of tamarugite.
The steam-condensate alteration paragenesis includes native sulphur,
bassanite, anhydrite,
epsomite, pickeringite,
halotrichite, apjohnite and
alunite, as well as quartz and
halite, all
primary and secondary speleogenetic by-products
(EJM 25.3.479–486).
At Compton Chine, Freshwater, Isle of Wight, England, UK, tamarugite occurs as yellow, red and occasionally white
encrustations on a vertical surface of tectonically disturbed beds of bluish black
pyrite-bearing siltstone. Whilst
most occurrences of water-soluble tamarugite have been reported from arid environments, there is a minority of
others on coastal sections where the influence of salt water spray is constant.
It is proposed that the production of H2SO4 from oxidising
pyrite in the siltstone
releases Al ions from the argillaceous sediments, the Na content being acquired from sea spray
(MM 62.3.371-372.).
At Fulton, Callaway county, Missouri, USA, tamarugite has been found altering from
mendozite
(Dana).
At Eureka, St. Louis county, Missouri, USA, tamarugite occurred as a white, fluffy to granular powder in varying
degrees of compactness on the west-facing side of a recently excavated road cut in
dolostone. A section of
dolostone about 10 feet in thickness and fifty yards long is exposed in
the cut. Ground water migrating down the slope of the hill and seeping out on this surface would be dried by the mid-day
and afternoon sunshine. The evaporating water, fed by seepage and capillarity, would leave behind its soluble load as a
residue on the surface. This deposited on the limestone surface as a
white powdery coating, thickening to a friable porous encrustation.
Other than impurities of fine quartz,
dolomite and clay, the
encrustation was found to consist of mendozite, that alters in air to
tamarugite
(AM 20.537-539).
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