Fossilized Bivalve Cross-Section in Sandstone Pebble
Bivalvia indet. cf. internal mold • Body fossil / Mold and cast (invertebrate)
Geological Period
Cretaceous
Estimated Age
66 to 145 million years
Preservation Type
Silicification and internal internal sediment fill / natural mold
Condition Assessment
Good condition. It is a naturally weathered pebble preserving a clean cross-sectional slice, though lacking complete exterior ornamentation due to water-rolling and erosion.
Taxonomic Classification
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Various, Genus: Indeterminate
Morphological Description
The specimen exhibits a natural cross-section showing the internal cavity and umbo region of a bivalve shell. The concentric growth lines and the distinct outline of the closed valves are visible as a lighter calcitic or quartz-filled ring contrasting against the surrounding porous sandstone matrix.
Rock Matrix
Fine-grained quartz sandstone with a weathered, porous exterior surface
Formation & Location
Coastal or river-rounded sedimentary deposits, commonly found in marine sedimentary formations worldwide
Size & Dimensions
Approximately 3 cm to 4 cm across, consistent with small to medium-sized shallow marine bivalves
Value & Rarity
Estimated Market Value
$10 - $30
Auction Estimate
$15 - $50
Rarity Assessment
Common
Scientific Significance
Provides evidence of past shallow marine environments and depositional energy, illustrating taphonomic processes where shell interiors become infilled with sediment prior to complete dissolution.
Preparation Recommendations
No active preparation needed as the specimen has been naturally tumbled and exposed by weathering. Store in a dry environment.
Notable Features
The smooth, water-worn pebble naturally cross-sections the fossilized shell, creating a clear bullseye-like pattern that highlights the internal morphology without requiring mechanical preparation.