Pyritized gastropods are fossils where the original shell material has been replaced or coated by pyrite in an anaerobic, iron-rich marine environment. Collectors should look for a brilliant, brassy metallic luster and well-defined internal whorls that retain the shape of the original mollusk. They are typically found in dark, organic-rich shales where oxygen levels were low during fossilization.
Is this pyritized gastropods?
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 pyritized gastropods with a known reference. Pyritized Gastropods sits at Mohs 3.5-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pyritized Gastropods leaves a greenish-black streak.
- 3Read the lusterHold the specimen under a strong light. Pyritized Gastropods typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: brass yellow, gold, brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: pseudomorphs after organic shell structures.
Often found alongside pyritized gastropods
Minerals reported to co-occur with pyritized gastropods. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeS₂
- Mohs hardness
- 3.5-4
- Density
- 4.8-5.1 g/cm³
- Colors
- Streak
- Greenish-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Pseudomorphs After Organic Shell Structures
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Lapidary
- Host rock
- Sedimentary Shale and Clay Beds
- Typical price
- $10-200 per specimen
Where rockhounds find pyritized gastropods
1 mapped spotsClassic worldwide localities
- France
- Germany
- United Kingdom
- Russia
- USA
Field-hunting tip
Look in sedimentary shale and clay beds country — that is the host setting where pyritized gastropods typically forms. If you start seeing pyrite, calcite, shale in float, you are in the right ground. Field specimens usually show a pseudomorphs after organic shell structures habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Illinois — start trip planning there.
Common questions
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Find pyritized gastropods on the map
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