Horn Coral (Rugose Coral)
Rugose coral cf. order Rugosa • Body fossil, invertebrate marine organism
Geological Period
Devonian (or Ordovician to Permian)
Estimated Age
359 to 419 million years old
Preservation Type
Permineralization and calcitic/silicic replacement within a limestone matrix
Condition Assessment
Good condition, showing moderate weathering on the exterior matrix and outer wall, but with a well-preserved and clear calice cross-section
Taxonomic Classification
Phylum: Cnidaria, Class: Anthozoa, Order: Rugosa
Morphological Description
Solitary horn-shaped corallite displaying a prominent circular calice (oral opening) at the top with visible radial septa radiating from a central point, enclosed in a weathered, rugose outer wall with longitudinal striations.
Rock Matrix
Buff-to-tan weathered limestone/dolostone matrix with irregular encrusting secondary mineral deposits
Formation & Location
Midcontinent North America, Corniferous or Onondaga Limestone formations, or similar Paleozoic shallow marine shelf deposits
Size & Dimensions
Approximately 7-9 cm in length and 4-5 cm in width at the calice, consistent with typical medium-sized solitary rugose corals
Value & Rarity
Estimated Market Value
$15 - $40 USD
Auction Estimate
$10 - $30 USD
Rarity Assessment
Common, widely distributed globally in Paleozoic marine sedimentary sequences
Scientific Significance
Provides insights into ancient Paleozoic shallow tropical marine ecosystems, reef structures, and historical marine biodiversity and paleoclimatology via sclerochronology
Preparation Recommendations
Mechanical cleaning using a soft brush and gentle water rinse; optional ultrasonic cleaning if matrix is stable; store in a dry environment
Notable Features
Particularly clear and circular transverse view of the septa within the calice standing out in stark contrast against the heavily weathered and pitted surrounding rock matrix