sedimentary

Banded Chert (River Siltstone)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale); Color: Dark grey to charcoal with lighter horizontal banding; Luster: Dull to waxy when unpolished; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Dark grey to charcoal with lighter horizontal banding
Luster: Dull to waxy when unpolished

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich organic or chemical remains in marine or lake environments. Over millions of years (often Paleozoic to Mesozoic era), heat and pressure compress the silt and silica into dense rock with visible layering called banding.

Uses & applications

Historically used for stone tools due to sharp edges; currently used for decorative gravel, landscaping, or as tumbled stones for hobbyist collectors.

Geological facts

Chert and its varieties like jasper and flint were the primary materials for human technology for thousands of years. The banding represents seasonal or environmental shifts during sediment deposition.

Field identification & locations

Identify in the field by its smooth, water-worn texture and distinct layers. It is harder than steel and will scratch a glass plate. Commonly found in riverbeds and glacial till throughout North America and Europe.