sedimentary
Chert / Chalcedony
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 (Mohs), Color: Gray, tan, brown, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/Cryptocrystalline, No cleavage, Conchoidal fracture
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Gray, tan, brown, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/Cryptocrystalline, No cleavage, Conchoidal fracture
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms) or chemical precipitation in marine environments, often replacing calcium carbonate in limestone.
Uses & applications
Historical use for stone tools (lithics), modern use in landscaping, construction aggregate, and occasionally as semi-precious gemstones or lapidary rough.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allowed for the creation of razor-sharp edges on arrows and spearheads.
Field identification & locations
Identify by its waxy texture, hardness (it will scratch glass), and edges that break like thick glass or obsidian. Commonly found in riverbeds or as nodules within limestone outcrops.
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Other sedimentary specimens
Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
fossil
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite
sedimentary
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary