Belemnite rostrum (Thunderbolt fossil)
cf. Hibolites sp. or Cylindroteuthis sp. • Body fossil; internal calcitic skeleton of an extinct cephalopod (Invertebrate)
Geological Period
Jurassic to Cretaceous
Estimated Age
66 to 201 million years
Preservation Type
Replacement/Recrystallization; original aragonite/calcite structure often replaced by stable calcite or sometimes silicated
Condition Assessment
Good; showing typical water-worn or weathered surface with one end broken or incomplete, typical for beach-found specimens
Taxonomic Classification
Phylum: Mollusca, Class: Cephalopoda, Order: Belemnitida, Family: Belemnitidae
Morphological Description
Cylindrical, bullet-shaped calcitic guard (rostrum) featuring a smooth surface with longitudinal grooves (striae) and a rounded distal apex. The proximal end typically shows a phragmocone cavity.
Rock Matrix
Specimen is extracted; likely originated from marine shale, limestone, or marl
Formation & Location
Commonly found in the Oxford Clay (UK), Solnhofen Limestone (Germany), or the Pierre Shale (USA)
Size & Dimensions
Approximately 4-6 cm in length; consistent with mid-sized Jurassic/Cretaceous belemnoid taxa
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $30.00 USD (typically sold in bulk lots)
Rarity Assessment
Common; widely distributed globally in Mesozoic marine deposits
Scientific Significance
Important index fossils for dating marine strata; provides data on Mesozoic marine food webs and paleotemperatures through oxygen isotope analysis
Preparation Recommendations
No specialized preparation needed; clean with water and a soft brush. Keep away from acidic cleaning agents which can dissolve calcite.
Notable Features
Distinctive dark coloration and high-density calcitic structure; the presence of apical grooves helps distinguish genus-level identity.