These are ancient ammonite fossils where the original calcium carbonate shell has been replaced by pyrite through mineral precipitation in anoxic, iron-rich sediments.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.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Ammonites (subclass Ammonoidea). Age: Early Devonian to the end of the Cretaceous.
- 3Check the preservationPreservation: Aragonite shell replaced by pyrite. That controls the weight, the hardness and how the piece takes a polish.
- 4Read the lusterHold the specimen under a strong light. Luster: metallic.
- 5Match the color rangeCompare against the expected color range: brass yellow, metallic gold, bronze.
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
- Mohs hardness
- 3-3.5
- Density
- 4.8-5.1 g/cm³
- Colors
- Luster
- Metallic
- Transparency
- Opaque
- Rarity
- Uncommon
- Uses
- Collector, Educational, Decorative
- Host rock
- sedimentary shale and clay deposits
- Organism
- Ammonites (subclass Ammonoidea)
- Age
- Early Devonian to the end of the Cretaceous
- Preservation
- Aragonite shell replaced by pyrite
Where rockhounds find pyritized ammonite
Classic worldwide localities
- Bully Brook, UK
- Volga River, Russia
- Uzbekistan
- Madagascar
- France
Field-hunting tip
Where it forms: sedimentary shale and clay deposits. If you start seeing calcite, shale, clay in float, you are in the right ground.
Common questions
How do you identify pyritized ammonite?+
Where is pyritized ammonite found?+
What rocks look like pyritized ammonite?+
What minerals are found with pyritized ammonite?+
What kind of rock does pyritized ammonite form in?+
What is pyritized ammonite used for?+
Find pyritized ammonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
