sedimentary

Chert (Jasper variation)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Brown, reddish-brown, and grey; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline) Quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, reddish-brown, and grey
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in marine settings or as nodules in limestone/chalk. This specimen appears water-worn, likely from a fluvial (river) or beach environment.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include jewelry, lapidary arts, and decorative landscaping rock.

Geological facts

Chert is so hard it can strike sparks against steel. It is one of the most durable sedimentary rocks and often survives long-distance transport in rivers and along coasts.

Field identification & locations

Identify by its hardness (cannot be scratched by a knife), waxy luster when broken, and characteristic conchoidal (shell-like) fracture. Commonly found in riverbeds and gravel pits.