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, so 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, so 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, 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.
