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Millerite

Millerite is a nickel sulfide mineral with the chemical formula NiS. It forms slender, acicular crystals that commonly aggregate in radiating clusters within hydrothermal sulfide veins.

It crystallizes in the hexagonal system and often exhibits a NiAs-type structure. Millerite occurs most notably

The mineral has a metallic luster and a steel gray to bronze color, tarnishing to brownish or

Millerite is of interest primarily as a minor nickel ore and as a mineralogical indicator in sulfide

in
nickel-copper
sulfide
ore
deposits
in
ultramafic
and
mafic
rocks,
and
it
is
commonly
associated
with
pyrrhotite,
pyrite,
pentlandite,
and
chalcopyrite.
black
surfaces.
Its
streak
is
gray
to
black.
Mohs
hardness
is
about
3.5
to
4,
and
the
specific
gravity
ranges
from
about
7.6
to
7.8.
It
shows
little
to
no
cleavage
and
tends
to
fracture
conchoidally.
deposits.
It
is
typically
formed
in
hydrothermal
environments
and
can
be
an
indicator
of
nickel-rich
ore
systems.