sedimentary

Chert / Jasper

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-tan; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, tan, and reddish-tan
Luster: Dull to waxy

Identified June 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-tan; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen shows a weathered surface with iron oxide staining.

Uses & applications

Used historically for stone tools and arrowheads; currently used as aquarium gravel, in construction as road base, and occasionally as decorative landscaping stone.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges used for hunting and cutting.

Field identification & locations

Identify by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture under the weathered exterior. Found globally in limestone formations.