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. Streak: grayish or brownish black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: pale brass-yellow, tin-white, gray, bronze, light brass yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: globular, stalactitic, tabular.
Often confused with
Marcasite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Marcasite leaves grayish or brownish black, Pyrite leaves greenish black to brownish black.
How to tell apart: Streak differs, so Marcasite leaves grayish or brownish black, Arsenopyrite leaves black.
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
- 4.887 g/cm³
- Streak
- Grayish or brownish black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Globular, stalactitic, tabular
- Cleavage
- {101}, rather distinct; {110} in traces
- Rarity
- Common
- Uses
- Collector, Decorative
- Host rock
- Typically formed under low-temperature highly acidic conditions, both in sedimentary environments (shales, limestones, and low rank coals) and in hydrothermal veins formed by ascending solutions
Where rockhounds find marcasite
62 mapped spotsClassic worldwide localities
- Joplin, Jasper Co., Missouri, USA
- Picher and Cardin, Ottawa Co., Oklahoma, USA
- Baxter Springs and Galena, Cherokee Co., Kansas, USA
- Mineral Point, Iowa Co., and Racine, Racine Co., Wisconsin, USA
- Vintířov, Litmice, Most, Osek, Czech Republic
- Clausthal, in the Harz Mountains, and Freiberg and Annaberg, Saxony, Germany
U.S. states with marcasite
Each link opens a state-specific list of mapped rockhounding spots that produce marcasite.
Field-hunting tip
Where it forms: Typically formed under low-temperature highly acidic conditions, both in sedimentary environments (shales, limestones, and low rank coals) and in hydrothermal veins formed by ascending solutions. If you start seeing pyrite, pyrrhotite, galena in float, you are in the right ground. Typical habit: globular, stalactitic, tabular. 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.
More marcasite photos
Common questions
How do you identify marcasite?+
Where is marcasite found?+
Can I find marcasite in the United States?+
What rocks look like marcasite?+
What minerals are found with marcasite?+
What kind of rock does marcasite form in?+
What is marcasite used for?+
Find marcasite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
