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Formula: (Ca,Cu,Na,Fe3+,Al)12Al2(AsO4)8(OH,Cl)x.nH2O
Valence: (Ca,Cu2+,Na,Fe3+,Al)12Al2(As5+O4)8(OH,Cl)x.nH2O
Hydrated arsenate, copper- and
ferric iron- bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.03 measured, 2.98 calculated
Hardness: May be 2 to 3
Streak: White
Colour: Pale blue
Luminescence: Not fluorescent
Solubility: Readily soluble without effervescence in 10% hydrochloric acid at room temperature
Environments
Barahonaite-(Al) occurs as a secondary mineral in the
oxidised zone of sulphide deposits. Associated minerals
include arsenocrandallite,
arsenogoyazite,
conichalcite,
cobaltarthurite,
chlorargyrite, olivenite,
azurite, cornwallite,
pharmacosiderite, jarosite,
zálesíite and lavendulan
(HOM).
Localities
At the type locality, La Reconquistada claim, Pastrana, Mazarrón, Murcia, Spain, the oxidation minerals occur as
coatings and within closely spaced fractures in weathered siliceous and micaceous host-rocks.
Pharmacosiderite and
jarosite are the most intimately associated with
barahonaite-(Fe) and barahonaite-(Al). Beads of
barahonaite-(Al) from Spain are only locally coalesced into aggregates of a few beads.
Barahonaite-(Fe) occurs sparingly as isolated, rosette-like beads, up
to about 200 microns across. The mineral forms sparse coatings on fracture surfaces, generally on a substrate of
pharmacosiderite, and coalescences of glittering beads are the norm
rather than the exception. The surface of the beads of
barahonaite-(Fe) and barahonaite-(Al) consists of razor-thin,
tabular, composite crystals whose maximum length is about 20 microns.
The macroscopically distinct difference between barahonaite-(Fe) and
barahonaite-(Al) is that the latter is pale blue and has a white streak, whereas
barahonaite-(Fe), owing to its much higher Fe content, is greenish
yellow and has a white to pale yellow streak. Both minerals have a vitreous lustre and are brittle, transparent to
translucent, non-fluorescent, and are readily soluble without effervescence in 10% hydrochloric acid at room
temperature.
Grains of barahonaite-(Fe) are 5 to 10 microns in maximum dimension.
Single-crystal portions of barahonaite-(Al) are only ~1 micron
(CM 46.1.205-217).
Barahonaite-(Al) from La Reconquistada claim -
Image
At the Gold Hill Mine, Gold Hill, Gold Hill Mining District, Tooele County, Utah, USA, although both
barahonaite-(Fe) and barahonaite-(Al) occur at the Dolores
prospect, only barahonaite-(Al) is present at Gold Hill. The Gold Hill mine, which has been inactive for more
than 50 years, produced modest tonnages of polymetallic ores (Pb–Cu–Ag–Au, including As derived from
arsenopyrite) in skarn and
post-skarn replacement veins and bodies. Nearly all of the
primary sulphides near the surface have been altered to
arsenate and sulphate assemblages; one of the
arsenate suites has been found to contain barahonaite-(Al).
Barahonaite-(Al) from Utah, although rare, is more abundant than at the Spanish occurrence. The Utah material
forms thin, smooth crusts of submillimetric thickness on weathered surfaces of fractures. The crusts are gradational to
areas at which the surface of the coatings is hemispherical and glistens because of the presence of microscopic platy
crystals. The plates are commonly curved, and their maximum size is about 50 microns across and less than 1 micron in
thickness. Commonly associated with the Utah material is a clear to faintly bluish, glassy, almost amorphous Al silicate
upon which crusts of barahonaite-(Al) have been deposited.
Arsenocrandallite is locally associated with the crusts
(CM 46.1.205-217).
Barahonaite-(Al) from the Gold Hill Mine -
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