sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Tan, dark brown, and black banding. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.7.

Hardness: 6
Color: Tan, dark brown, and black banding
Luster: Waxy to dull

Identified March 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite by silica-rich fluids. Common in Precambrian to Cenozoic strata.

Uses & applications

Historically used for stone tools (knapping) due to sharp edges; currently used for road surfacing, as grinding media in ball mills, and occasionally in lapidary work for jewelry like cabochons.

Geological facts

Chert was one of the most important minerals for early humans, used to create arrowheads, spears, and striking stones to create sparks for fire. It is exceptionally durable and resistant to chemical weathering.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture and being hard enough to scratch glass. Commonly found as nodules in limestone beds or as rounded pebbles in stream beds and coastal areas.

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Brecciated Chert (Microcrystalline Silica)

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