sedimentary
Chert (Arrowhead/Tool Grade)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Mottled brown, grey, and black with translucent edges; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Mottled brown, grey, and black with translucent edges
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Mottled brown, grey, and black with translucent edges; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in limestone or chalk beds. Often Paleozoic or Mesozoic in age.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for decorative stone, flint-knapping enthusiasts, and occasionally in the construction of road bases.
Geological facts
Chert exhibits conchoidal fracture, meaning it breaks like glass to produce razor-sharp edges. This piece shows signs of intentional flaking or 'knapping,' suggesting it may be a lithic debitage or tool fragment.
Field identification & locations
Identify in the field by its waxy texture, inability to be scratched by a steel blade, and sharp, shell-like fracture patterns. Commonly found in stream beds or eroding out of limestone outcrops.
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