Millerite is best known for its distinct hair-like, acicular crystal habit that forms delicate, radiating clusters of brassy needles. It is often found as inclusions or sprays lining cavities within carbonate host rocks like limestone or dolostone.
Is this millerite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch millerite with a known reference. Millerite sits at Mohs 3-3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Millerite leaves a bright greenish-black streak.
- 3Read the lusterHold the specimen under a strong light. Millerite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: brass-yellow, pale bronze-yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: acicular, capillary, hair-like bundles, radiating sprays.
Often confused with
Millerite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Millerite leaves bright greenish-black, Heazlewoodite leaves blackish.
How to tell apart: Streak differs — Millerite leaves bright greenish-black, Pentlandite leaves light bronze-brown.
How to tell apart: Streak differs — Millerite leaves bright greenish-black, Chalcopyrite leaves greenish-black.
Often found alongside millerite
Minerals reported to co-occur with millerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NiS
- Mohs hardness
- 3-3.5
- Density
- 5.3-5.6 g/cm³
- Streak
- Bright Greenish-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Acicular, Capillary, Hair-like Bundles, Radiating Sprays
- Cleavage
- Good in Three Directions
- Rarity
- Uncommon
- Uses
- Collector, Specimen
- Host rock
- Sedimentary Carbonate Rocks, Hydrothermal Veins, Nickel-rich Massive Sulfide Deposits
- Typical price
- $15-200 depending on specimen size and clarity of needle sprays
Where rockhounds find millerite
7 mapped spotsClassic worldwide localities
- Sudbury Basin, Ontario, Canada
- Czech Republic
- Belgium
- USA (Kentucky, Missouri)
Field-hunting tip
Look in sedimentary carbonate rocks, hydrothermal veins, nickel-rich massive sulfide deposits country — that is the host setting where millerite typically forms. If you start seeing calcite, dolomite, fluorite in float, you are in the right ground. Field specimens usually show a acicular, capillary, hair-like bundles, radiating sprays habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, Wisconsin — start trip planning there.
Common questions
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Find millerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
