Septarian Nodule Segment (Pseudosuchian / Geode Mineralization)
Inorganic sedimentary feature (commonly mistaken for fossilized bone, wood, or turtle shell) • Inorganic Concretion / Septarian Structure (Not a fossil)
Geological Period
Cretaceous (commonly found in Late Cretaceous strata)
Estimated Age
50 to 100 million years old
Preservation Type
Mineral crystallization within shrinkage fractures (Dehydration-derived septarian veining)
Condition Assessment
Fair; partial broken fragment of a larger septarian concretion showing exposed crystalline core
Taxonomic Classification
Non-biological (Sedimentary Geologic Structure / Mineral Nodular Aggregate)
Morphological Description
Angular fragment showing brownish claystone/mudstone exterior host rock interrupted by internal septarian cracking network (shrinkage cracks). Internal cavities are lined with crystalline white-to-grey calcite and microcrystalline quartz/chalcedony.
Rock Matrix
Iron-rich mudstone/siltstone exterior matrix filled with white calcite and chalcedony/quartz crystallization
Formation & Location
Commonly found in Late Cretaceous marine shale formations such as the Mancos Shale (Utah, USA), Pierre Shale (Midwestern USA), or similar worldwide basin deposits (e.g., Madagascar, UK)
Size & Dimensions
Approximately 8 to 12 cm in length and 4 to 6 cm in width
Value & Rarity
Estimated Market Value
$5 - $15 USD
Auction Estimate
$10 - $20 USD
Rarity Assessment
Common (frequently found globally in sedimentary shale and clay beds)
Scientific Significance
Demonstrates diagenetic processes in ancient marine muds, specifically clay desiccation, mud dehydration, mineral migration, and secondary crystal precipitation within nodular cavities.
Preparation Recommendations
No scientific prep required. Light cleaning with warm water and soft brush. Keep dry to prevent oxidation of iron compounds.
Notable Features
Angular mosaic patterning created by calcite-filled shrinkage cracks intersecting an iron-stained mudstone matrix, featuring small druzy calcite crystal cavity in the center.