Brachiopod (Lamp Shell)
cf. Spirifer sp. • Body fossil; Marine Invertebrate
Geological Period
Devonian to Carboniferous (Mississippian)
Estimated Age
320 to 410 million years
Preservation Type
Recrystallization/Replacement; the original calcium carbonate shell has likely been replaced by more stable calcite or silica.
Condition Assessment
Good; showing clear ribbing and hinge structure, though some weathering is present on the outer margins.
Taxonomic Classification
Phylum: Brachiopoda, Class: Rhynchonellata, Order: Spiriferida, Family: Spiriferidae
Morphological Description
Sub-triangular to semi-elliptical shell shape with a distinct long hinge line. Surface exhibits strong radial ribbing (costae) and a visible central fold and sulcus characteristic of spiriferid brachiopods.
Rock Matrix
Specimen is extracted/loose, but originally likely associated with limestone or calcareous shale.
Formation & Location
Common in the Mahantango Formation (USA), various Moroccan Devonian beds, and the limestone deposits of the UK and Belgium.
Size & Dimensions
Approximately 2.5 to 4 cm in width; typical size for a mature spiriferid individual.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $30.00 USD (typically sold in bulk lots for scientific study or beginners)
Rarity Assessment
Common; Brachiopods are among the most prolific Paleozoic fossils found worldwide.
Scientific Significance
Index fossils used for biozonation; provides data on Paleozoic marine benthic communities and ancient water depths/currents.
Preparation Recommendations
Mechanical cleaning with a soft brush; store in a dry environment. No high-level conservation required due to stable mineral state.
Notable Features
Well-defined radial costae and a prominent 'wing-like' hinge line which gave this group the nickname 'butterfly shells'.