sedimentary

Chert (variations include Flint or Jasper)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: tan, grey, cream with banding; Luster: waxy to dull; Crystal Structure: Cryptocrystalline (hexagonal system); Cleavage: none, exhibits conchoidal fracture; Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: tan, grey, cream with banding
Luster: waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the ocean floor or by the replacement of limestone by silica-rich fluids. Can be found in rock layers dating from the Precambrian to the present.

Uses & applications

Historically used for stone tools and arrowheads; today used in construction aggregate, road surfacing, and as a durable material in lapidary work.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be broken into tools with edges sharper than a steel scalpel. It is also sparks when struck against steel, making it vital for fire-starting.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth waxy feel, and curved 'shell-like' fracture surfaces. Common in limestone regions and gravel pits.