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Formula: CoFe
Alloy of cobalt and iron
Crystal System: Isometric
Specific gravity: 8.32 calculated
Hardness: 5
Colour: Steel-grey
Magnetism: Strongly magnetic
Common impurities: Ni
Environments
Wairauite belongs to the association of serpentinisation which
contains such minerals as
awaruite, iron and
heazlewoodite, mostly connected with plentiful
secondary magnetite
(Ramdohr p358).
Localities
At the type locality, Red Hills, Wairau Valley, Marlborough Region, New Zealand, wairauite occurs in
serpentinite in a large
ultramafic intrusion. Associated minerals include
chromite, magnetite,
awaruite and native copper. Both
awaruite and wairauite form very small grains distributed throughout
the serpentinite close to the contact. They are occasionally
concentrated in late serpentine veins and around the margins of
serpentine pseudomorphs after
olivine. Grains rarely exceed 5 microns across and most are less than 2 microns,
the largest found being 7 X 4 microns.
Wairauite and awaruite are found only in the
serpentinite and have never been observed in unaltered
ultramafic rocks at Red Hills.
Indications are that the formation of the
nickel-iron and
cobalt-iron minerals is not associated
with an introduction of nickel or cobalt
and that the material necessary for their formation could have come from the
serpentinisation of the
olivine. The presence of grains of wairauite and
awaruite outlining serpentine
pseudomorphs after olivine, and in
the late veins of serpentine, supports the view that the formation of these
minerals is closely connected with the serpentinisation process.
The serpentines in which the alloys are found at Red Hills are dominantly
lizardite, with a notable poverty of
nickel and cobalt. The association of
cobalt-iron and
nickel-iron alloys and
native copper in the Red Hills
serpentinite indicates strongly reducing conditions and an absence
of sulphur during
serpentinisation
(MM 33.942-948).
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