Marcasite is a polymorph of pyrite, often recognized by its distinct cockscomb or spear-shaped twinned crystals. It is prone to oxidation, meaning specimens should be kept in a dry, low-humidity environment to prevent the crystal structure from breaking down into white powdery sulfates.
Is this marcasite?
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 marcasite with a known reference. Marcasite sits at Mohs 6-6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Marcasite leaves a greyish-black streak.
- 3Read the lusterHold the specimen under a strong light. Marcasite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: pale brass-yellow, tin-white, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, cockscomb aggregates, spear-shaped twins, massive.
Often confused with
Marcasite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside marcasite
Minerals reported to co-occur with marcasite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeS₂
- Mohs hardness
- 6-6.5
- Density
- 4.8-4.9 g/cm³
- Streak
- Greyish-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Cockscomb Aggregates, Spear-shaped Twins, Massive
- Cleavage
- Poor
- Rarity
- Common
- Uses
- Collector, Decorative
- Host rock
- Sedimentary Rocks, Hydrothermal Veins
- Typical price
- $5-50 for small clusters, up to $200 for aesthetic display specimens
Where rockhounds find marcasite
61 mapped spotsClassic worldwide localities
- Joplin, Missouri, USA
- Naica, Mexico
- Cap Griz-Nez, France
- Clausthal, Germany
- Dover, England
U.S. states with marcasite
Each link opens a state-specific list of mapped rockhounding spots that produce marcasite.
Field-hunting tip
Look in sedimentary rocks, hydrothermal veins country — that is the host setting where marcasite typically forms. If you start seeing pyrite, galena, sphalerite in float, you are in the right ground. Field specimens usually show a tabular crystals, cockscomb aggregates, spear-shaped twins, massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, Indiana, Wisconsin — start trip planning there.
Common questions
How do you identify marcasite?+
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Can I find marcasite in the United States?+
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Find marcasite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
