Calamites (Giant Horsetail) Stem
Calamites cf. suckowii • Body fossil/Compression; Plant classification (Sphenopsid)
Geological Period
Carboniferous (Pennsylvanian sub-period)
Estimated Age
298.9 to 323.2 million years
Preservation Type
Compression and carbonization within an iron-rich mineralized matrix. Surface detail is preserved as an impression or mold of the external bark or inner pith.
Condition Assessment
Fair to Good. The vertical ribbing is identifiable, but the specimen is weathered and the edges are fragmentary. Partial node preservation.
Taxonomic Classification
Kingdom: Plantae, Phylum: Pteridophyta, Class: Equisetopsida, Order: Equisetales, Family: Calamitaceae, Genus: Calamites
Morphological Description
Specimen shows a longitudinal segment of a pith cast or flattened stem. Distinctive features include parallel vertical ribbing (striae) and a visible node (horizontal line) where leaf whorls or branches would have attached. The ribs are blunt and aligned across the nodes.
Rock Matrix
Ferruginous (iron-stained) silty shale or siderite-rich mudstone, typical of Coal Measures strata.
Formation & Location
Likely from the Coal Measures Group of the United Kingdom (e.g., South Wales or Yorkshire) or the Mazon Creek/Appalachian formations of North America.
Size & Dimensions
Approximately 6-8 cm in length; representative of a medium-sized stem segment of a plant that could reach 30 meters height.
Value & Rarity
Estimated Market Value
$15 - $35 USD
Auction Estimate
$20 - $50 USD
Rarity Assessment
Common. Calamites stems are frequently found in Carboniferous coal-bearing strata worldwide.
Scientific Significance
Provides evidence of the 'Coal Forests' of the Paleozoic. Calamites were major contributors to global coal deposits and represent an extinct lineage of giant scouring rushes that occupied swampy tropical environments.
Preparation Recommendations
Mechanical cleaning with a soft brush to remove loose debris. Consolidation with a dilute reversible adhesive (like Paraloid B-72) if the shale is prone to flaking. Keep in a low-humidity environment to prevent pyrite decay.
Notable Features
Heavy iron-oxide staining gives the specimen a distinct reddish-brown 'terracotta' color, which highlights the relief of the vertical vascular bundles.