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Formula: (Ni,Fe)9S8
Sulphide, pentlandite group, forms a series with
cobaltpentlandite
Crystal System: Isometric
Specific gravity: 4.6 to 5 measured, 4.956 calculated
Hardness: 3½ to 4
Streak: Pale bronze-brown
Colour: Pale bronze-yellow; bronze; brown; reddish brown when argentian
Solubility: Insoluble in 1:1 hydrochloric acid Dana
Common impurities: Co,Ag,Cu
Environments
Plutonic igneous environments
Metamorphic environments
Meteorites
Pentlandite is the most abundant nickel mineral. It forms through
magmatic segregation in
mafic and ultra-mafic
plutonic igneous rocks (AES, Webmin) with iron and nickel sulphides
and arsenides, almost always associated with pyrrhotite (Dana). It
is also found in mantle xenoliths and undersea “blacksmoker" deposits, and rarely in stony meteorites
(HOM).
Associated minerals include pyrrhotite,
troilite, chalcopyrite,
cubanite, mackinawite and
magnetite
(HOM).
Localities
There are two co-type localities, the Espedalen mines, Gausdal, Oppland, Norway, and the Craignure Mine, Inveraray,
Argyll and Bute, Scotland, UK
(Mindat).
At the Francistown District, North-East District, Botswana, there are several
nickel deposits, most of which contain
pentlandite,
pyrrhotite,
chalcopyrite and pyrite
(BC).
At Saint-Pierre-de-Broughton, Les Appalaches RCM, Chaudière-Appalaches, Quebec, Canada, in the Alpine-type fissures
and talc
deposit, pentlandite is the only nickel mineral found thus far, occuring
as inclusions in
foliated masses of
talc in the talc-carbonate
schist
(R&M 85.6.505).
At the Hunting Hill quarry, Rockville, Maryland, USA, pentlandite is found in
serpentine with minor magnetite
and talc (Minrec 36.5.444), but this reference does not mention
pyrrhotite from this locality.
In Zimbabwe pentlandite usually occurs with other nickel minerals, notably
millerite, at several nickel deposits in
ultramafic rocks
(BC).
Alteration
The transformation of pentlandite to violarite has been investigated under
mild hydrothermal conditions, at constant
values of pH (3 to 5, quite acid). At 80oC, 20% by weight of the pentlandite transforms to
violarite in 33 days
(AM 91.706-709).
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