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
62 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, 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.
