Ammonite Fossil Fragment with Pyritization
Ammonoidea indet. cf. Ammonite family (fragmentary) • Body fossil, invertebrate cephalopod, preserved as a mineralized fragment with partial replacement.
Geological Period
Jurassic to Cretaceous
Estimated Age
66 to 201 million years
Preservation Type
Partial permineralization and mineral replacement, with iron sulfides (pyrite/marcasite) and amber-colored calcitic/aragonitic shell layers visible along the edge.
Condition Assessment
Fair to Good. Fragmentary and heavily weathered or partially matrix-obscured, but retaining interesting mineralogical details along the edges.
Taxonomic Classification
Phylum: Mollusca, Class: Cephalopoda, Subclass: Ammonoidea, Order: Ammonitida
Morphological Description
Exhibits curved chamber walls and septa characteristic of the phragmocone of an ammonoid cephalopod. Outer whorl segments display subtle indications of ribbing and suture line traces partially obscured by matrix and mineral encrustation.
Rock Matrix
Dark, fine-grained argillaceous limestone or calcareous shale matrix, showing secondary metallic oxidation and mineral crusting.
Formation & Location
Commonly found in marine sedimentary formations globally, such as the Oxford Clay (UK), Solnhofen Limestone (Germany), or various Cretaceous formations in North America and Madagascar.
Size & Dimensions
Approximately 4 cm to 6 cm across the visible preserved sector, representing a small fragment of a larger original specimen.
Value & Rarity
Estimated Market Value
$25 - $75 USD
Auction Estimate
$20 - $50 USD
Rarity Assessment
Common
Scientific Significance
Provides insights into ammonoid internal chamber structure, septal development, and the taphonomic processes of pyritization and fossil diagenesis in marine environments.
Preparation Recommendations
Gentle mechanical cleaning with a soft brush or air abrasive unit using fine powder to reveal more suture lines without damaging the delicate mineralized outer layers. Store in a low-humidity environment to prevent pyrite decay.
Notable Features
The striking contrast between the dark oxidized matrix and the translucent amber-hued mineralized shell edge, along with hints of metallic pyrite replacement.