sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Reddish-brown, tan, opaque; Luster: Waxy to dull; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.91

Hardness: 6
Color: Reddish-brown, tan, opaque
Luster: Waxy to dull

Identified April 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation within sedimentary rock layers, often occurring as nodules or beds in limestone or chalk. Many specimens are millions of years old.

Uses & applications

Used historically for stone tools and arrowheads due to its sharp edges when fractured. Today, it is used as an ornamental stone, in gemstone tumbling, and for primitive fire-starting (flint).

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture allows for the creation of razor-sharp edges. 'Jasper' is the term specifically used for opaque, colored varieties, usually red due to iron inclusions.

Field identification & locations

Identify in the field by its extreme hardness (will scratch glass), its waxy texture, and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, gravel pits, and eroding out of limestone cliffs.