Millerite (NiS) is nickel sulfide forming distinctive bronze-yellow acicular needles — sometimes capillary-thin and meters-long. It crystallizes in low-temperature hydrothermal vug fillings and as a late-stage alteration of nickel-bearing sulfides. The Halls Gap (Kentucky) Mississippian limestone vugs and Lancaster County (Pennsylvania) classic localities supply iconic acicular specimens.
Key Facts
- Mohs hardness 3–3.5.
- Trigonal; capillary acicular and hair-like needle habit is diagnostic.
- Bronze-yellow color with vitreous-metallic luster.
- Forms in low-T hydrothermal cavities in carbonates and ultramafics.
- Common in serpentinite-hosted Ni deposits.
Notable Localities
Halls Gap (Kentucky) and Lancaster County (Pennsylvania) yield iconic acicular needles. Sterling Hill (New Jersey) supplies fluorescent specimens.
Found at these Localities
- Tri-State Mining District (Joplin) (三州矿区(乔普林))
