Rudist Bivalve Mold / Cast
Rudist bivalve indet. (cf. Requienia or Toucasia) • Internal mold and cast (steinkern), invertebrate body fossil
Geological Period
Cretaceous
Estimated Age
66 to 145 million years ago
Preservation Type
Natural internal mold (steinkern) with calcitic replacement and recrystallization within the matrix.
Condition Assessment
Fair to Good. Weathered surface with a clear internal mold impression, though outer margins are heavily eroded and incomplete.
Taxonomic Classification
Phylum: Mollusca, Class: Bivalvia, Order: Hippuritida, Family: Requieniidae or Caprinidae, Genus: undetermined
Morphological Description
The specimen exhibits a prominent, roughly conical or cup-shaped central depression representing the internal cavity (steinkern) of a lower valve, surrounded by a thick, recrystallized calcitic outer wall impression with rough, irregular surface contours and concentric growth lines.
Rock Matrix
Light-colored, fine-grained fossiliferous limestone with minor crystalline calcite secondary mineralization lining the inner cavity.
Formation & Location
Commonly found in Cretaceous shallow marine carbonate platforms, such as the Edwards Formation in Texas, or Tethyan Cretaceous limestone deposits of Southern Europe and the Middle East.
Size & Dimensions
Approximately 5 to 7 centimeters across, which is typical for medium-sized juvenile to adult individual requieniid rudists.
Value & Rarity
Estimated Market Value
$10 - $30 USD
Auction Estimate
$15 - $40 USD
Rarity Assessment
Common, widely distributed in Cretaceous limestone deposits worldwide.
Scientific Significance
Rudists were major reef-building organisms during the Cretaceous period before going extinct at the Cretaceous-Paleogene boundary. This fossil provides insight into tropical shallow-water marine carbonate shelf paleoenvironments.
Preparation Recommendations
Gentle mechanical cleaning with a soft brush to remove loose surface matrix. Store in a dry environment. No complex conservation treatments required.
Notable Features
Clear central conical steinkern cavity showing the distinct asymmetry typical of sessile reef-dwelling rudist bivalves.