sedimentary

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, or black (often mottled); Luster: Waxy to dull; Structure: Cryptocrystalline (non-visible crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, white, or black (often mottled)
Luster: Waxy to dull

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich biogenic material (like radiolarian or sponge spicules) on the ocean floor, or through chemical precipitation in groundwater. Geological age ranges from Precambrian to Cenozoic.

Uses & applications

Used historically for stone tools and weapons (arrowheads) due to its sharp edges. Modernly used in road construction, as flint for fire-making, and occasionally as semi-precious gemstones or 'river rock' landscaping.

Geological facts

Because of its conchoidal fracture pattern, it breaks like glass into razor-sharp edges. It was arguably the most important mineral for early human survival for both hunting tools and fire starting.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy feel, and smooth curved (conchoidal) surface where broken. Common in limestone beds. Look for it in riverbeds and dry creek beds where it often survives weathering better than surrounding rocks.

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