Tabulate Coral (Honeycomb Coral)
Favosites cf. hamiltoniae • Body fossil of a colonial marine invertebrate
Geological Period
Devonian (possibly Silurian)
Estimated Age
360 to 420 million years
Preservation Type
Recrystallization with replacement by silica (typical of Michigan Devonian corals) or calcite. The specimen shows significant weathering from water transport.
Condition Assessment
Fair. The specimen is heavily weathered and water-worn, which has softened the sharp anatomical details, though the internal tabulae are still visible in the fracture plane.
Taxonomic Classification
Phylum: Cnidaria, Class: Anthozoa, Order: Tabulata, Family: Favositidae, Genus: Favosites
Morphological Description
Small fragment of a colonial honeycomb coral exhibiting characteristic polygonal (hexagonal or pentagonal) corallites. The cross-section reveals closely packed vertical tubes divided by horizontal plates called tabulae, which appear as the layered, wave-like structures visible in the broken section.
Rock Matrix
The specimen is largely free of its original limestone or shale matrix, appearing as a water-worn pebble composed primarily of the coral skeletal material itself.
Formation & Location
Commonly found in the Traverse Group formations of Michigan; specimen likely transported via glacial drift or Lake Erie wave action to Sterling State Park.
Size & Dimensions
Approximately 3-4 cm in length. This is a small fragment of what would have originally been a larger, mound-shaped colony.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $20.00 USD (as part of a bulk lot of Great Lakes fossils)
Rarity Assessment
Common. Favositid corals are ubiquitous throughout the Great Lakes region and are frequently collected along lake shorelines.
Scientific Significance
Favosites are index fossils for the Silurian and Devonian periods. They represent the massive reef-building environments that covered the Michigan Basin when it was a warm, shallow tropical sea near the equator.
Preparation Recommendations
No further mechanical preparation is recommended. To enhance the detail of the corallites, the specimen can be briefly dipped in a mild acid solution or coated with a light mineral oil to increase contrast.
Notable Features
The specimen clearly shows the internal 'tabulae' (floors) within the individual coral tubes where the polyps once lived, revealed by a natural break in the structural skeleton.
Notes
Found at Sterling State Park in Michigan