sedimentary

Chert / Jasper

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, and grey with possible iron staining; Luster: Dull to waxy when dry, vitreous when wet; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brown, tan, and grey with possible iron staining
Luster: Dull to waxy when dry, vitreous when wet

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and grey with possible iron staining; Luster: Dull to waxy when dry, vitreous when wet; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary layers. This specimen shows significant river-wear or water-action rounding.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; currently used for lapidary work, decorative landscaping, and as a collector's specimen.

Geological facts

Chert is so durable that it often survives long-distance transport in rivers and glacial deposits. When it is red or highly colored, it is referred to as Jasper.

Field identification & locations

Look for a smooth, waxy texture and conchoidal (shell-like) fractures. It is commonly found in riverbeds, coastal areas, and limestone outcrops throughout the United States and globally.