sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and reddish-orange due to iron oxides; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.6-2.7

Hardness: 6
Color: Brown, tan, and reddish-orange due to iron oxides
Luster: Waxy to dull

Identified April 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and reddish-orange due to iron oxides; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich microfossils or via chemical precipitation from silica-rich fluids within sedimentary rock layers like limestone. This specimen appears to have undergone significant iron staining during or after formation.

Uses & applications

Used historically for stone tools and arrowheads; currently used as ornamental stones, in jewelry (cabs), and as landscaping/fill material.

Geological facts

Chert is so durable that it often survives as 'float' in stream beds long after the surrounding limestone has eroded away. Historically, high-quality cherts were some of the most traded materials among early human civilizations.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its shell-like (conchoidal) fracture pattern, and its smooth, waxy texture compared to the surrounding rock. Common in limestone-rich regions.