Mackinawite is a rare iron nickel sulfide that usually occurs as microscopic inclusions within other sulfide minerals. It is best known to collectors as an accessory phase in massive sulfide ores and is characterized by its distinct bronze color and metallic luster.
Is this mackinawite?
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 mackinawite with a known reference. Mackinawite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Mackinawite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Mackinawite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: bronze, yellowish-brown, gray.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: massive, lamellar, or microscopic grains.
Often confused with
Mackinawite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Pyrrhotite is the harder of the two (Mohs 3.5-4.5 vs. 2.5); streak differs — Mackinawite leaves black, Pyrrhotite leaves dark grey to black.
How to tell apart: Pentlandite is the harder of the two (Mohs 3.5-4 vs. 2.5); streak differs — Mackinawite leaves black, Pentlandite leaves light bronze-brown.
How to tell apart: Streak differs — Mackinawite leaves black, Chalcocite leaves lead-gray to black.
Often found alongside mackinawite
Minerals reported to co-occur with mackinawite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Fe,Ni)₁₊ₓS
- Mohs hardness
- 2.5
- Density
- 4.15-4.23 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Massive, Lamellar, Or Microscopic Grains
- Cleavage
- Perfect
- Rarity
- Uncommon
- Uses
- Collector, Research
- Host rock
- Mafic and Ultramafic Igneous Rocks, Hydrothermal Veins
- Typical price
- $20-100 for small samples
Where rockhounds find mackinawite
Classic worldwide localities
- Mackinaw Mine, Washington, USA
- Bushveld Complex, South Africa
- Sudbury, Ontario, Canada
- Norilsk, Russia
Field-hunting tip
Look in mafic and ultramafic igneous rocks, hydrothermal veins country — that is the host setting where mackinawite typically forms. If you start seeing pyrrhotite, pentlandite, chalcopyrite in float, you are in the right ground. Field specimens usually show a massive, lamellar, or microscopic grains habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mackinawite?+
Where is mackinawite found?+
How much is mackinawite worth?+
What rocks look like mackinawite?+
What minerals are found with mackinawite?+
What kind of rock does mackinawite form in?+
What is mackinawite used for?+
Find mackinawite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
