Fossilized Stromatoporoid or Coral Pebble
Stromatoporoidea indet. (cf. Actinostroma or similar reef-building colonial organism) • Body fossil / Invertebrate marine organism
Geological Period
Silurian to Devonian
Estimated Age
443 to 359 million years ago
Preservation Type
Permineralization and complete silicification or calcification within a rounded water-transported clast
Condition Assessment
Fair to Good. Highly water-worn and weathered external surface, heavily abraded with no original outer morphology remaining, but internal micro-structure is partially visible via weathering lines.
Taxonomic Classification
Phylum: Cnidaria, Class: Hydrozoa, Order: Stromatoporida
Morphological Description
Water-worn, rounded pebble exhibiting fine internal concentric laminations and vertical pillars characteristic of stromatoporoid sponge-like structures or colonial rugose/tabulate corals, with a heavily pitted upper weathering surface.
Rock Matrix
Silicified limestone / dolostone matrix
Formation & Location
Glacial till deposits, river gravels, or ancient shallow marine carbonate platforms globally (e.g., Midwest United States, Northern Europe)
Size & Dimensions
Approximately 4 to 6 cm in maximum dimension, typical of a small cobble-sized fossil fragment
Value & Rarity
Estimated Market Value
$5 - $15 USD
Auction Estimate
$10 - $25 USD
Rarity Assessment
Common. Such fossiliferous pebbles are frequently found in glacial drift and river gravels in regions with Paleozoic limestone bedrock.
Scientific Significance
Provides evidence of ancient shallow tropical marine reef environments and paleo-ecosystems during the Paleozoic era when calcareous sponges and colonial corals dominated reef building.
Preparation Recommendations
No aggressive preparation needed. Can be washed gently with water and a soft brush. Keep dry and store at room temperature.
Notable Features
Distinct parallel banding/lamination visible on the lower flank caused by differential weathering of the colonial skeletal layers.