Silicified Marine Invertebrate Cluster / 'Pudding' or 'Gumball' Chert
Indeterminate Brachiopod/Bivalve fragments preserved in chert (cf. Composita or similar brachiopod genus) • Body fossil and mold combination (Invertebrate Marine)
Geological Period
Likely Mississippian to Pennsylvanian (Carboniferous Period)
Estimated Age
299 to 350 million years
Preservation Type
Silicification (Replacement by silica) and mineralization featuring drusy quartz crystal coatings.
Condition Assessment
Fair; the specimen is highly weathered and lacks fine anatomical detail due to coarse silicification and erosion.
Taxonomic Classification
Phylum: Brachiopoda or Mollusca; Class: Articulata (potential shell fragments)
Morphological Description
Irregularly shaped nodule with visible convex shell outlines and interior voids. The surface is granular and drusy, showing microcrystalline quartz growth. Concave features suggest where shell material once rested before partial replacement.
Rock Matrix
Chert (Siliceous sedimentary rock) with internal iron oxide staining giving it a tan to reddish-brown hue.
Formation & Location
Burlington Limestone or Keokuk Limestone (Midwestern USA) or similar Paleozoic marine limestone deposits.
Size & Dimensions
Approximately 3-5 cm in maximum dimension; typical for small nodular chert inclusions.
Value & Rarity
Estimated Market Value
$5 - $15 USD
Auction Estimate
$10 - $25 USD (as part of a bulk lot)
Rarity Assessment
Common; these types of chert nodules are frequently found in gravel deposits and limestone outcrops across the American Midwest and UK.
Scientific Significance
Low; provides a record of localized silica replacement processes in Paleozoic marine beds and paleoenvironmental fluid chemistry.
Preparation Recommendations
No further mechanical preparation suggested. A mild soap and water cleaning is sufficient. Best displayed as a 'hands-on' educational specimen.
Notable Features
Secondary drusy quartz growth in the vugs (cavities) provides a slight crystalline sparkle, which is a classic indicator of late-stage mineralized replacement.