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Formula: Fe2+Al2(SO4)4.22H2O
Sulphate, halotrichite group, forms a series with
pickeringite
Crystal System: Monoclinic
Specific gravity: 1.89 measured, 1.95 calculated
Hardness: 1½ to 2
Streak: White
Colour: Colourless to white, yellowish, greenish; colourless in transmitted light
Solubility: Completely soluble in water to an acid solution
Environments
Hydrothermal environments
Fumeroles and hot springs
Halotrichite occurs as efflorescences in weathering sulphide deposits and oxidising
pyritic coals, with persistent accumulations in arid climates; also as a precipitate
around volcanic fumaroles and hot springs. Associated minerals include melanterite,
copiapite, gypsum,
epsomite and alunogen
(HOM).
Localities
The Sherritt Gordon Mine, Sherridon District, Manitoba, Canada, was mined for zinc,
copper, silver and
gold between 1930 and 1951. Since mine closure, two high-sulphide tailings impoundments
underwent extensive oxidation, resulting in the release of very high concentrations of dissolved sulphate and metals to the
tailings porewater. During precipitation events and Spring freshet, surface seeps develop along the flanks of the impoundments,
discharging groundwater with a pH as low as 0.39 (extremely acid) and dissolved concentrations of sulphate and iron up to
203 gm/litre and 68 gm/litre respectively, along with other metals at elevated concentrations. Secondary efflorescent sulphate
minerals at seepage zones included melanterite,
rozenite, halotrichite,
chalcanthite, alpersite,
copiapite, hexahydrite,
jurbanite, pickeringite,
jarosite and gypsum
(CM 53.5.961-977).
At the Sydney coalfield, Cape Breton County, Nova Scotia, Canada, hydrated sulphates associated with decomposition of
pyrite and
copper-iron sulphides occur in coal in contact with
the atmosphere. Melanterite, rozenite,
epsomite, pickeringite, halotrichite,
aluminocopiapite and sideronatrite
were identified from coal seams and mines
(CM 16.17-22)
At Dolliver State Park, Webster County, Iowa, USA, abundant sulphate efflorescences on
sandstone have previously been considered to consist of
melanterite. Further analysis has now shown that they consist of halotrichite,
szomolnokite and rozenite.
Melanterite may occur in place of the lower hydrate,
rozenite, during times of high humidity
(CM 11.958-970).
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