sedimentary

Chert (River Pebble)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs. Color: Dull grey, olive-green, or brownish. Luster: Waxy to dull. Structure: Microcrystalline with conchoidal fracture. Cleavage: None. Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Dull grey, olive-green, or brownish
Luster: Waxy to dull

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs. Color: Dull grey, olive-green, or brownish. Luster: Waxy to dull. Structure: Microcrystalline with conchoidal fracture. Cleavage: None. Specific Gravity: 2.6-2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen has been rounded and smoothed by water erosion in a stream or river bed.

Uses & applications

Historically used for arrowheads and scrapers due to its sharp edges when broken. Today used as decorative gravel, in road construction, and as aquarium stones.

Geological facts

Chert is a very hard and durable rock that can survive long periods of transport in rivers. It is essentially the same material as flint, but the term flint is usually reserved for nodules found in chalk or limestone.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy feel. Often found in riverbeds, gravel pits, and sedimentary outcrops globally.