sedimentary
Fossiliferous Chert (with Brachiopod or Mollusk fragments)
Silicon dioxide (SiO2) with Calcium Carbonate (CaCO3) inclusions
Hardness: 6.5-7 (scratches glass); Color: Grayish-green to brown matrix with white fossil inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Conchoidal fracture common in larger pieces.
- Hardness
- 6
- Color
- Grayish-green to brown matrix with white fossil inclusions
- Luster
- Dull to waxy
Identified More sedimentary →
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Physical properties
Hardness: 6.5-7 (scratches glass); Color: Grayish-green to brown matrix with white fossil inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Conchoidal fracture common in larger pieces.
Formation & geological history
Formed through the accumulation of silica-rich marine organisms (like diatoms or radiolaria) on the ocean floor, which later undergoes diagenesis. The embedded fossils (white fragments) were trapped during the solidification process. Often found in Paleozoic or Mesozoic strata.
Uses & applications
Used historically for tool making (due to sharp edges when fractured), as a decorative stone, and currently as a subject for geological study and fossil collecting.
Geological facts
Chert is a chemical sedimentary rock that can preserve fine details of ancient marine life. The white rings or 'loops' seen in this specimen are cross-sections of fossilized shells that have been partially or fully replaced by minerals.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and the presence of visible fossil remains against a fine-grained matrix. Commonly found in riverbeds, glacial tills, and limestone outcrops.
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