These are ancient ammonite fossils where the original calcium carbonate shell has been replaced by pyrite through mineral precipitation in anoxic, iron-rich sediments. Collectors prize them for their striking metallic luster and intricate detail of the fossilized chambers. They are typically found in marine shale formations where lack of oxygen prevented decay and allowed for specific mineral replacement.
Is this pyritized ammonite?
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 ammonite with a known reference. Pyritized Ammonite sits at Mohs 3-3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pyritized Ammonite leaves a greenish-black streak.
- 3Read the lusterHold the specimen under a strong light. Pyritized Ammonite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: brass yellow, metallic gold, bronze.
- 5Look at form & habitCrystal system: isometric. Typical habit: replacement of organic structures with cubic pyrite crystals.
Often confused with
Pyritized Ammonite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside pyritized ammonite
Minerals reported to co-occur with pyritized ammonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeS₂
- Mohs hardness
- 3-3.5
- Density
- 4.8-5.1 g/cm³
- Streak
- Greenish-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Isometric
- Crystal habit
- Replacement of Organic Structures with Cubic Pyrite Crystals
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Educational, Decorative
- Host rock
- Sedimentary Shale and Clay Deposits
- Typical price
- $20-300 depending on preservation and size
Where rockhounds find pyritized ammonite
Classic worldwide localities
- Bully Brook, UK
- Volga River, Russia
- Uzbekistan
- Madagascar
- France
Field-hunting tip
Look in sedimentary shale and clay deposits country — that is the host setting where pyritized ammonite typically forms. If you start seeing calcite, shale, clay in float, you are in the right ground. Field specimens usually show a replacement of organic structures with cubic pyrite crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pyritized ammonite?+
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What rocks look like pyritized ammonite?+
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Find pyritized ammonite on the map
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