Internal Mold of a Gastropod (Steinkern)
Incomplete mold; resembles cf. Rostellaria or cf. Tylostoma depending on original whorl morphology • Body fossil/Internal mold; Invertebrate Gastropod
Geological Period
Likely Cretaceous or Paleogene
Estimated Age
Approx. 50 to 100 million years
Preservation Type
Recrystallization and internal molding (Steinkern). The original calcium carbonate shell is absent, replaced by or filled with lithified sediment.
Condition Assessment
Fair; the specimen is incomplete, missing the apex and the aperture, and shows heavy weathering/abrasion.
Taxonomic Classification
Phylum: Mollusca, Class: Gastropoda, Order: Unidentifiable (likely Neogastropoda or Caenogastropoda), Genus/Species: Indeterminate
Morphological Description
Smooth, rounded internal casting showing two partial whorls. The specimen is an internal mold (steinkern) where the original shell has dissolved, leaving a sediment-filled interior. It lacks external ornamentation such as ribs or original shell color.
Rock Matrix
Fine-grained chalky limestone or calcarenite; the fossil is largely composed of the matrix material itself.
Formation & Location
Commonly found in the Chalk Group of Western Europe (UK/France) or the Glen Rose/Edwards Formations of Texas, USA.
Size & Dimensions
Approximately 2-3 cm in diameter; typical for small to medium-sized mesozoic/cenozoic marine snails.
Value & Rarity
Estimated Market Value
5 USD - 15 USD
Auction Estimate
Not typically a standalone auction item; likely sold in bulk lots of 20 USD - 40 USD
Rarity Assessment
Common; internal molds of gastropods are among the most frequently occurring marine fossils in limestone deposits.
Scientific Significance
Provides evidence of local paleo-marine environments and sedimentology; indicates high-energy or chemically active post-depositional environments where shells are commonly dissolved.
Preparation Recommendations
No further preparation required; store in a dry environment and handle carefully as chalky matrix can be friable.
Notable Features
Clean, globose shape of the body whorl and a distinct 'steinkern' appearance which clearly demonstrates how fossils fill with sediment.