sedimentary

Chert (Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grey, blue-grey, or tan; Luster: Waxy to dull; Structure: Microcrystalline silicon dioxide; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grey, blue-grey, or tan
Luster: Waxy to dull

Identified March 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, blue-grey, or tan; Luster: Waxy to dull; Structure: Microcrystalline silicon dioxide; 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 in sedimentary basins. It often occurs as nodules in limestone or chalk beds. Geological age ranges from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges when fractured. Modern uses include road construction aggregate, fire-starting strikers (flint), and tumbling for lapidary use/jewelry.

Geological facts

Chert was one of the most important materials for early humans; it produces a spark when struck against steel. The 'conchoidal fracture' allows it to break into razor-sharp edges, a property shared with obsidian and glass.

Field identification & locations

Identify in the field by its waxy luster, hardness (it will scratch glass), and its distinctive curved (conchoidal) breaks. It is commonly found in riverbeds, along beaches, or embedded in limestone cliffs.