Calamites Stem Fragment (Horsetail Fossil)
Calamites sp. (cf. C. suckowii based on ribbing frequency) • Body fossil (impression/compression of plant matter), Paleobiology: Archegonian vascular plant
Geological Period
Carboniferous (specifically Pennsylvanian sub-period)
Estimated Age
298.9 to 323.2 million years
Preservation Type
Carbonization and Adpression. The dark material represents a thin film of carbonized organic matter, while the structure is preserved as an impression in an iron-rich matrix.
Condition Assessment
Fair to Good. The ribbing is distinct, but the specimen is a fragmentary section lacking nodal junctions and is partially obscured by matrix weathering.
Taxonomic Classification
Kingdom: Plantae, Division: Pteridophyta, Class: Equisetopsida, Order: Equisetales, Family: Calamitaceae, Genus: Calamites
Morphological Description
Specimen shows parallel longitudinal ribbing (striae) characteristic of the internal or external pith cast of a giant horsetail. The ribs are slightly flattened and separated by narrow furrows. No visible nodes (joints) are apparent in this specific fragment, indicating it is an internodal segment.
Rock Matrix
Ironstone nodules or Sideritic Mudstone; characterized by a distinct reddish-brown (limonitic/hematitic) oxidation on the surface with a dark, carbon-rich interior.
Formation & Location
Likely the Mazon Creek Formation (Illinois, USA) or the Coal Measures of the United Kingdom and Western Europe.
Size & Dimensions
Approximately 5-7 cm in length; consistent with mid-sized branch fragments of the Calamites tree which could reach 30+ meters.
Value & Rarity
Estimated Market Value
USD $15.00 - $35.00
Auction Estimate
USD $20.00 - $50.00 as part of a multi-specimen lot
Rarity Assessment
Common. Calamites fragments are ubiquitous index fossils in Carboniferous coal-bearing strata worldwide.
Scientific Significance
Provides evidence of the 'Coal Forest' swamp ecosystems of the Paleozoic era. Calamites were major contributors to global coal deposits and represent an evolutionary peak in sphenopsid size and complexity.
Preparation Recommendations
Mechanical cleaning with a soft brush to remove loose oxidation; stabilize with a thin coat of Paraloid B-72 if the carbon film is flaking. Keep in a low-humidity environment to prevent pyrite decay if present.
Notable Features
The high contrast between the dark carbonaceous film and the orange-red oxidized ironstone matrix is aesthetically pleasing and typical of siderite-preserved flora.