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

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).


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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