Mazon Creek Plant Fossil (Neuropteris leaf segment/branch fragment)
Neuropteris cf. rarinervis • Body fossil / Carbonization and Impression (Plant)
Geological Period
Carboniferous (Pennsylvanian subperiod)
Estimated Age
307 - 309 million years
Preservation Type
Carbonaceous film within a siderite (iron carbonate) concretion, exhibiting secondary iron oxide replacement (limonite/hematite) giving it a distinct reddish hue.
Condition Assessment
Fair to Good; the specimen is a partial fragment of a larger concretion with some weathering. The detail is obscured by the rough fracture of the matrix.
Taxonomic Classification
Kingdom: Plantae, Phylum: Pteridospermatophyta (Seed Ferns), Order: Medullosales, Family: Neuropteridaceae, Genus: Neuropteris
Morphological Description
The specimen shows partial leaf morphology with hints of pinnule structure. The stem or rachis is visible as a reddish-orange line, with flattened organic material appearing as dark carbonized films and iron oxide staining against the grey host rock.
Rock Matrix
Siderite concretion matrix (grey ironstone) showing natural weathering and fracture planes common in the Francis Creek Shale.
Formation & Location
Francis Creek Shale Member of the Carbondale Formation, Mazon Creek area, Illinois, USA.
Size & Dimensions
Approximately 5 to 7 cm in width; typical for small to medium-sized concretion fragments from this locality.
Value & Rarity
Estimated Market Value
$15 - $35 USD
Auction Estimate
$20 - $50 USD (typically sold in lots or at specialized local mineral shows)
Rarity Assessment
Common; while specific species vary in rarity, Neuropteris is one of the most frequently encountered genera in the Mazon Creek flora.
Scientific Significance
Crucial for understanding the 'Coal Forest' ecosystems of the Late Paleozoic; provides data on coastal deltaic flora and the diversity of extinct seed-bearing ferns.
Preparation Recommendations
Keep dry to prevent oxidation; occasional cleaning with a soft brush. If more of the specimen is buried, mechanical air-scribing or the freeze-thaw method (for un-opened nodules) is usually employed.
Notable Features
Distinctive reddish-orange mineralization contrasting against the dark grey siderite; provides a clear example of the characteristic preservation found in the Braidwood Biota.