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Formula: Mg(SO4).7H2O
Hydrated sulphate, melanterite group
Crystal System: Monoclinic
Specific gravity: 1.820 calculated
Hardness: 2½
Streak: White
Colour: Blue, pale blue, whitish
Common impurities: Cu,Zn,Mn,Fe
Environments
Alpersite is an efflorescent secondary mineral, likely
widespread and unnoticed in mine wastes that contain copper-bearing sulphides,
but in which solubilised Fe2+ is not available for melanterite
crystallisation because of oxidation to Fe3+ in surface waters of near-neutral pH. Associated minerals
include pickeringite, alunogen,
epsomite and gypsum
(HOM).
Localities
The former Sherritt Gordon Mine, Sherridon District, Manitoba, Canada, was mined for
zinc, copper,
silver and gold. 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. Several
secondary efflorescent sulphate minerals at seepage zones were
identified, including melanterite,
rozenite, halotrichite,
chalcanthite, alpersite,
copiapite, hexahydrite,
jurbanite, pickeringite,
jarosite and gypsum
(CM 53.961-977).
At the type locality, the Big Mike mine, Tobin and Sonoma Range Mining District, Pershing county, Nevada, USA,
alpersite, a mineral species with direct relevance to reactions in mine waste, occurs in a mineralogically
zoned assemblage in sheltered areas at the abandoned Big Mike mine, at a relative humidity of 65% and temperature
4oC. Blue alpersite, which is isostructural with
melanterite, is overlain by a light blue to white layer dominated by
pickeringite, alunogen and
epsomite.
It is suspected that alpersite and copper-bearing
pentahydrite are widespread in mine wastes that contain
copper-bearing sulphides, but in which solubilised Fe2+ is not
available for melanterite crystallisation because of oxidation to
Fe3+ in surface waters of near-neutral pH
(AM 91.261-269).
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