sedimentary
Chert (Nodule/Pebble)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, earthy; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, earthy
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, earthy; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. This specimen is a water-worn nodule, likely from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges. Currently used in construction aggregate, road surfacing, and as tumbling media for lapidary hobbies.
Geological facts
Chert was one of the most important minerals for early humans. Its ability to fracture conchoidally into razor-sharp edges made it the 'high-tech' material of the Stone Age. It is chemically identical to quartz but has a different micro-structure.
Field identification & locations
Identify in the field by its hardness (will scratch glass and steel), waxy texture when wet, and smooth, curved (conchoidal) break patterns. Often found in riverbeds, glacial till, or eroding out of sedimentary rock layers.
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