sedimentary

Chert (or Jasper)

Silicon dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, and dark grey swirling bands; Luster: Dull to waxy; Texture: Fine-grained, cryptocrystalline; Breakage: Conchoidal fracture.

Hardness: 6
Color: Brown, tan, and dark grey swirling bands
Luster: Dull to waxy

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and dark grey swirling bands; Luster: Dull to waxy; Texture: Fine-grained, cryptocrystalline; Breakage: Conchoidal fracture.

Formation & geological history

Formed by the accumulation of silica-rich microfossils or chemical precipitation in marine or groundwater environments. This pebble appears water-worn, smoothed by river or coastal erosion.

Uses & applications

Historically used for making stone tools (arrowheads). Currently used for lapidary work, landscaping, and as a component in construction aggregate.

Geological facts

Chert is essentially an impure form of flint. When it is red or orange-hued due to iron inclusions, it is often called Jasper. It is one of the most durable sedimentary rocks.

Field identification & locations

Identify in the field by its hardness (will scratch glass) and smooth, shell-like fracture patterns. Often found in riverbeds or as nodules within limestone or chalk deposits.