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. Streak: greenish black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: brass yellow, bronze, greenish gray, gray.
- 5Look at form & habitCrystal system: trigonal. Typical habit: acicular, massive.
Often confused with
Millerite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Millerite leaves greenish black, Heazlewoodite leaves light bronze.
How to tell apart: Streak differs, so Millerite leaves greenish black, Pentlandite leaves pale bronze-brown.
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
- 5.5 g/cm³
- Streak
- Greenish black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Acicular, massive
- Cleavage
- Perfect on {1011} and {0112}
- Rarity
- Uncommon
- Uses
- Collector, Specimen
- Host rock
- Most commonly as a low-temperature mineral, in cavities in limestones and carbonate veins and in barite; an alteration product of other nickel minerals
Where rockhounds find millerite
8 mapped spotsClassic worldwide localities
- Sterling mine, Antwerp, Jefferson Co., New York, USA
- Gap Nickel mine, Lancaster Co., Pennsylvania, USA
- Geodes from Keokuk, Lee Co., Iowa, USA
- St. Louis, St. Louis Co., Missouri, USA
- Germany (type locality), from Müsen and Wissen, and as Ramsbeck, North Rhine-Westphalia
- Kamsdorf, Thuringia
Field-hunting tip
Where it forms: Most commonly as a low-temperature mineral, in cavities in limestones and carbonate veins and in barite; an alteration product of other nickel minerals. If you start seeing gersdorffite, polydymite, nickeline in float, you are in the right ground. Typical habit: acicular, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, New York, Wisconsin. Start trip planning there.
More millerite photos
Common questions
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Find millerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
