sedimentary

Chert (Siliceous Pebble)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brownish-gray with subtle quartz veining; Luster: Waxy to dull, smooth river-worn texture; Fracture: Conchoidal; Specific Gravity: ~2.65

Hardness: 6
Color: Tan, beige, brownish-gray with subtle quartz veining
Luster: Waxy to dull, smooth river-worn texture

Identified July 26, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brownish-gray with subtle quartz veining; Luster: Waxy to dull, smooth river-worn texture; Fracture: Conchoidal; Specific Gravity: ~2.65

Formation & geological history

Formed through biochemical precipitation of silica from ancient marine organisms or primary inorganic chemical precipitation. Often stream-rounded and reworked into alluvial deposits in northeastern Pennsylvania (Ridge and Valley / Appalachian Plateau provinces).

Uses & applications

Historically used for stone tools and flintknapping; commonly used today in landscaping, aggregate, and as tumbled decorative pebbles.

Geological facts

Chert is extremely durable and resistant to weathering due to its dense microcrystalline quartz structure. Small pebbles with cross-cutting veinlets like this one are extremely common in riverbeds across Pennsylvania.

Field identification & locations

Identify by its hardness (scratches glass, steel file cannot scratch it), smooth conchoidal or waxy surfaces, and lack of visible mineral grains. Abundant in gravel deposits, stream beds, and till throughout North America.