millerite

{{Infobox mineral | name = Millerite | category = Sulfide mineral | boxwidth = | image = Millerite in geode (Hall's Gap, Kentucky, USA).jpg | imagesize = 260px | caption = | formula = NiS | IMAsymbol = Mlr | strunz = 2.CC.20 | system = Trigonal | class = Ditrigonal pyramidal (3m) (same H-M symbol) | symmetry = R3m | unit cell = a = 9.607 Å, c = 3.143 Å; Z = 9 | colour = Pale brass-yellow to bronze-yellow, tarnishes to iridescence | habit = Typically acicular (needle-like) often in radial sprays – also massive | cleavage = Perfect on {101} and {012} – obscured by typical form | fracture = Uneven | tenacity = Brittle; capillary crystals elastic | mohs = 3–3.5 | luster = Metallic | diaphaneity = Opaque | refractive = | pleochroism = | streak = Greenish black | gravity = 5.3–5.5 | melt = | solubility = | other = brittle and becomes magnetic on heating | references = }}

Millerite or nickel blende is a nickel sulfide mineral, NiS. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller colour, and general lack of association with pyrite or pyrrhotite.