Internal Mold of a Gastropod or Brachiopod Steinkern
Indeterminate genus et species • Body fossil (Internal Cast/Steinkern); Invertebrate
Geological Period
Likely Cretaceous or Jurassic
Estimated Age
Approx. 66 to 150 million years
Preservation Type
Internal mold (Steinkern); sediment filling of the original shell which then dissolved, leaving the interior cast.
Condition Assessment
Fair; the specimen is an eroded internal cast lacking external shell detail or diagnostic ornamentation.
Taxonomic Classification
Phylum: Mollusca (likely); Class: Gastropoda (potential); Phylum: Brachiopoda (potential alternative)
Morphological Description
Rounded, sub-globular form with a distinct central suture or whorl line suggesting a coiled or bivalved structure that has been filled with sediment and subsequently lithified. Surface is relatively smooth with some localized pitting and iron-oxide staining.
Rock Matrix
Fine-grained calcareous sandstone or calcarenite; likely cemented with calcium carbonate or silica.
Formation & Location
Commonly found in marine sedimentary layers such as the Glen Rose Formation (USA) or English Chalk deposits.
Size & Dimensions
Approximately 3-4 cm in diameter; consistent with medium-sized mesozoic marine invertebrates.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $30.00 USD (usually sold in bulk lots)
Rarity Assessment
Common; internal molds of this type are found in high frequency in many sedimentary basins globally.
Scientific Significance
Provides evidence of paleo-marine environments and taphonomic processes where calcium carbonate shells are more soluble than the infilling sediment.
Preparation Recommendations
No further mechanical preparation advised as the specimen lacks a shell. Store in a dry environment and clean with a soft brush.
Notable Features
The specimen exhibits a classic steinkern preservation, clearly showing the transition between the sediment fill and the plane where the original shell once resided.