sedimentary

Chert Pebble

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with possible banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, and grey with possible banding
Luster: Waxy to dull

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. This specimen appears water-worn from a stream or alluvial deposit.

Uses & applications

Historically used for stone tools and weapons due to sharp fractures. Currently used in road construction (aggregate), decorative landscaping, and occasionally as minor gemstones (gem silica).

Geological facts

Chert is so hard it can create sparks when struck against steel, a property that led to its use in flintlock firearms. It is chemically identical to quartz and amethyst but has much smaller crystal units.

Field identification & locations

Identify in the field by its smooth, waxy texture and curved (conchoidal) breaks that resemble glass. Common in riverbeds and limestone outcrops. Collectors look for unique banding or fossil inclusions.

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