Horn Coral (Rugose Coral)
Heliophyllum cf. halli or Zaphrentis sp. • Body fossil, invertebrate marine coral
Geological Period
Devonian to Ordovician (likely Devonian or Silurian based on common matrix and associations)
Estimated Age
359 to 443 million years old
Preservation Type
Permineralization and calcitic replacement with internal cavity infilling by secondary matrix and minerals
Condition Assessment
Good. The specimen shows clear structural details of the coral corallites embedded within the hard limestone matrix, with minor surface weathering and iron staining along fracture lines
Taxonomic Classification
Phylum: Cnidaria, Class: Anthozoa, Order: Rugosa, Family: Zaphrentidae, Genus: Heliophyllum cf. or similar solitary rugose coral
Morphological Description
Two distinct solitary rugose coral calices exposed in cross-section/oblique view within a block. Radiating septa are clearly visible, converging toward the center of the corallite. The larger specimen on the left shows prominent septal ridges and a conical horn-like shape, while the smaller specimen on the right shows a clear transverse cross-section highlighting the internal septal arrangement and central tabulae.
Rock Matrix
Fossiliferous limestone with argillaceous components and minor iron-oxide staining
Formation & Location
Commonly found in the Onondaga Formation of New York, Jeffersonville Limestone of the Midwest, or similar Paleozoic shallow marine shelf deposits in North America and Europe
Size & Dimensions
The matrix block is approximately 10 to 15 cm across. The larger coral calice measures roughly 4 to 5 cm in diameter, which is typical for mature solitary rugose corals of this group
Value & Rarity
Estimated Market Value
15 to 45 USD
Auction Estimate
20 to 50 USD
Rarity Assessment
Common. Solitary rugose corals are abundant globally in Paleozoic marine sedimentary formations
Scientific Significance
Provides valuable insight into Paleozoic shallow marine tropical environments, reef ecosystems, and the evolutionary history of early coral reef builders before the Permian-Triassic extinction event
Preparation Recommendations
Keep dry, store in a stable indoor environment, and minimal preparation needed as the fossils are already naturally exposed in the matrix. Mechanical scribing could be used to clean surrounding matrix if further exposure of the corallite exterior is desired
Notable Features
Contains multiple (at least two primary) solitary rugose coral specimens in a single host matrix block, offering both a transverse cross-sectional view of the internal septa and an oblique calice view for educational and display comparison