Inoceramus Shell Fragment
Inoceramus cf. balticus • Body fossil; Marine Invertebrate (Bivalve)
Geological Period
Upper Cretaceous
Estimated Age
66 to 100 million years
Preservation Type
Recrystallization; the original aragonitic layers have likely been lost, leaving the more stable calcitic prismatic layer preserved.
Condition Assessment
Fair; it is a weathered, incomplete fragment (clast) with worn edges and no remaining hinge structure.
Taxonomic Classification
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Inoceramidae, Genus: Inoceramus
Morphological Description
A flat, sub-quadrate fragment of a calcitic valve. It displays characteristic concentric growth undulations (rugae) and a distinct prismatic crystalline structure visible in the cross-section of the shell wall.
Rock Matrix
Matrix-free; likely weathered out from a soft chalk or marl matrix.
Formation & Location
Commonly found in the Pierre Shale (USA), Niobrara Formation (USA), or Cretaceous Chalk deposits of Europe (UK, France, Germany).
Size & Dimensions
Approximately 3-5 cm; a small fragment of a larger organism that could reach over 1 meter in diameter.
Value & Rarity
Estimated Market Value
$5 - $15 USD
Auction Estimate
$10 - $30 USD (as part of a bulk study lot)
Rarity Assessment
Common; Inoceramid fragments are ubiquitous in Cretaceous marine deposits worldwide.
Scientific Significance
Inoceramids are important index fossils for Cretaceous stratigraphy and provide data on ancient benthic marine environments and low-oxygen tolerance in epicontinental seas.
Preparation Recommendations
Requires no mechanical preparation. Store in a dry environment; keep away from acids which will dissolve the calcite.
Notable Features
Shows the classic 'honeycomb' prismatic structure of the Inoceramidae family, which often allows these shells to remain intact even when the surrounding rock erodes.