Rugose Coral (Horn Coral) Calyx or Internal Steinkern
Solitary rugose coral (Horn coral), cf. Zaphrentis sp. • Body fossil, solitary rugose coral internal mold/steinkern with prominent septal grooves
Geological Period
Ordovician to Permian (likely Devonian or Carboniferous based on typical preservation)
Estimated Age
300 to 400 million years old
Preservation Type
Internal mold (steinkern) with mineral replacement, showing fine textural details of the coral's internal septa imprinted onto the sediment fill
Condition Assessment
Good condition; a complete uncrushed steinkern exhibiting clear structural details with minor surface weathering and iron-staining
Taxonomic Classification
Phylum: Cnidaria, Class: Anthozoa, Order: Rugosa, Family: Various, Genus: cf. Zaphrentis or similar solitary rugose coral
Morphological Description
Conical to slightly curved horn-like shape with a prominent central longitudinal furrow (pseudoechinoid or cardinal septum impression) and radiating transverse ridges representing septal grooves and growth lines. The specimen shows a tapering apex and a rounded, swollen exterior surface typical of an internal mold or steinkern.
Rock Matrix
Iron-stained argillaceous limestone or calcareous mudstone with yellowish-brown limonite/goethite weathering oxidation
Formation & Location
Commonly found in Paleozoic marine sedimentary formations worldwide, such as the Silica Shale of Ohio, Jeffersonville Limestone, or various European Carboniferous limestone deposits
Size & Dimensions
Approximately 5 to 7 cm in length, consistent with medium-sized solitary rugose corals of the Paleozoic era
Value & Rarity
Estimated Market Value
$15 - $40 USD
Auction Estimate
$20 - $50 USD
Rarity Assessment
Common, widely distributed across global Paleozoic marine deposits
Scientific Significance
Provides insights into Paleozoic shallow marine benthic ecosystems, solitary coral growth habits, and reef or carbonate platform environments before the Permian-Triassic extinction event
Preparation Recommendations
Gentle mechanical cleaning with a soft brush to remove loose surface dirt; no harsh acid preparation required due to existing stable matrix and mineral composition; store in a dry environment to prevent further oxidation
Notable Features
Distinct deep central longitudinal groove running the length of the specimen, crisp transverse septal ridges, and warm golden-brown coloration due to natural iron oxide staining