Greigite is a rare magnetic iron sulfide that is the sulfur analog of magnetite. It is primarily found in sedimentary environments or as a product of low-temperature hydrothermal processes, often forming tiny octahedral crystals or massive crusts.
Is this greigite?
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 greigite with a known reference. Greigite sits at Mohs 4-4.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Greigite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Greigite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black, gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral, granular, massive.
Often confused with
Greigite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 4-4.5); streak differs — Greigite leaves black, Pyrite leaves greenish-black to brownish-black.
How to tell apart: Magnetite is the harder of the two (Mohs 5.5-6.5 vs. 4-4.5).
How to tell apart: Streak differs — Greigite leaves black, Pyrrhotite leaves dark grey to black.
Often found alongside greigite
Minerals reported to co-occur with greigite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₃S₄
- Mohs hardness
- 4-4.5
- Density
- 4.08 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Octahedral, Granular, Massive
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Sedimentary Environments, Hydrothermal Deposits, Anoxic Aquatic Sediments
- Typical price
- $20-100 per specimen
Where rockhounds find greigite
Classic worldwide localities
- California, USA
- Italy
- Hungary
- Poland
- China
Field-hunting tip
Look in sedimentary environments, hydrothermal deposits, anoxic aquatic sediments country — that is the host setting where greigite typically forms. If you start seeing pyrite, calcite, marcasite in float, you are in the right ground. Field specimens usually show a octahedral, granular, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find greigite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
