sedimentary

Chert / Jasper

Cryptocrystalline Silica (SiO2)

Hardness: 7 (Mohs scale), Color: tan, brown, reddish-brown, Luster: dull to waxy, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified June 9, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, brown, reddish-brown, Luster: dull to waxy, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation from fluids within sedimentary layers. Can be found in various geological ages from Precambrian to recent.

Uses & applications

Used historically for stone tools due to conchoidal fracture; modernly used as road aggregate, architectural stone, and occasionally in lapidary work or as river rock for landscaping.

Geological facts

This specimen shows significant iron oxide staining (limonite/hematite) giving it the reddish-brown patches. Chert is one of the most common materials used by early humans for making arrowheads and scrapers.

Field identification & locations

Identify in the field by its high hardness (it will scratch glass), smooth waxy feel on broken surfaces, and distinct curved (conchoidal) breakage patterns. Common in limestone and dolostone formations.