sedimentary

Chert / Jasper

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown, earthy dark tones with streaks; Luster: Dull to waxy; Texture: Microcrystalline, smooth conchoidal fracture patterns; Specific Gravity: 2.58–2.91.

Hardness: 6
Color: Reddish-brown, earthy dark tones with streaks
Luster: Dull to waxy

Identified June 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from seawater or the accumulation of silica-rich marine micro-organisms like radiolarians or diatoms. It can also form by replacement of other minerals in limestone.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today used as an abrasive, in landscaping, and as a semi-precious gemstone in jewelry.

Geological facts

Chert is so hard it can strike sparks against steel, which is why it was historically used in flintlock firearms. The red varieties, often colored by iron oxide, are commonly called Jasper.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by steel), smooth shell-like fracture surfaces, and fine-grained texture. It often occurs as nodules or layers within limestone and dolomite beds.