sedimentary

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Brown, gray, or black; Luster: Dull to waxy; Structure: Microcrystalline with no visible grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brown, gray, or black
Luster: Dull to waxy

Identified April 10, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, gray, or black; Luster: Dull to waxy; Structure: Microcrystalline with no visible grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or by the chemical precipitation of silica in sedimentary environments. Common in marine limestone formations.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Today used in construction aggregate, road surfacing, and occasionally as a gemstone (jasper).

Geological facts

Because of its conchoidal fracture, it produces extremely sharp edges, making it the primary material for prehistoric arrowheads and spear points. It is also famous for producing sparks when struck against steel.

Field identification & locations

Identify by its extreme hardness (will scratch glass) and its curved, glass-like fracture surfaces. Often found as nodules within limestone or as pebbles in riverbeds.