Invertebrate Impression / Shell Fragment
Incertae sedis; requires further preparation, possibly cf. Productus or cf. Aviculopecten • Body fossil (impression/mold); Invertebrate
Geological Period
Likely Carboniferous to Permian
Estimated Age
250 to 350 million years
Preservation Type
Impression with some iron oxide replacement/staining; mineralized mold
Condition Assessment
Poor to Fair; partial specimen, highly weathered, significant matrix coverage, and lack of fine diagnostic distal features
Taxonomic Classification
Phylum: Mollusca or Brachiopoda; Class: Bivalvia or Articulata
Morphological Description
Small, linear to fan-shaped ridges suggestive of shell ribs; slight convex curvature indicative of a valve surface; surface texture is weathered and partially obscured by matrix.
Rock Matrix
Ferruginous siltstone or dark grey shale/mudstone with secondary iron staining
Formation & Location
Commonly found in the Pennsylvanian/Mississippian marine deposits of the Midwestern USA or the UK coal measures
Size & Dimensions
Approximately 3-5 cm across; the visible fossil imprint is roughly 15-20 mm in length
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $20.00 USD (as part of a bulk study lot)
Rarity Assessment
Common; typical of fossiliferous marine shale or siltstone deposits
Scientific Significance
Low; serves as an indicator of a paleo-marine environment but lacks the detail required for significant evolutionary or stratigraphic study
Preparation Recommendations
Mechanical cleaning using a pin-tool or air-scribe may reveal more of the shell margin; keep dry and store in a labeled specimen box
Notable Features
Distinctive ferruginous (iron-rich) staining on the fossil surface which contrasts slightly with the darker matrix