Odessitoma or similar Gastropod Steinkern (Internal Mold)
Gastropoda indet. (requires clearer suture patterns for specific species designation) • Internal mold (Steinkern); Invertebrate gastropod
Geological Period
Likely Jurassic or Cretaceous, though some similar forms occur in Paleozoic strata
Estimated Age
Approximately 66 to 200 million years old
Preservation Type
Internal mold (steinkern) with mineral replacement; likely sphaerosiderite or phosphate-enriched mineralization given the dark, lustrous surface.
Condition Assessment
Fair to Good; despite the lack of original shell material (aragonite/calcite), the mold provides a clear representation of the internal whorl volume with some surface fracturing.
Taxonomic Classification
Phylum: Mollusca, Class: Gastropoda, Order: Uncertain, Genus: cf. Pleurotomaria or Glauconia (based on mold shape)
Morphological Description
Smooth, dark brown internal mold representing the sediment-filled cavity of a spiral shell; exhibits a low-spired, globose whorl profile with a subtle visible suture line and basal flattening.
Rock Matrix
Minimal remaining matrix; appears to have been weathered out of a fine-grained sedimentary rock like mudstone or marl.
Formation & Location
Commonly found in the English Gault Clay or similar Mesozoic marine deposits throughout Europe and North America.
Size & Dimensions
Approximately 1.5 cm to 2 cm in diameter; consistent with average sizes for small Mesozoic gastropods.
Value & Rarity
Estimated Market Value
$2 - $10 USD
Auction Estimate
$5 - $15 USD (usually sold in bulk lots)
Rarity Assessment
Common; internal molds of gastropods are ubiquitous in marine sedimentary deposits globally.
Scientific Significance
Provides data on local paleo-benthic communities and evidence of post-mortem taphonomic processes where shell dissolution occurs after sediment lithification.
Preparation Recommendations
No further chemical preparation needed; clean with a soft brush and store in a dry, stable environment to prevent possible pyrite oxidation if sulfur is present.
Notable Features
The specimen stands out for its dark, almost metallic luster, which suggests a high concentration of iron or phosphate during the fossilization process.