sedimentary
Chert (River Pebble)
Chert (Cryptocrystalline Quartz, SiO₂)
Hardness: 7 (Mohs scale), Color: dull gray to brownish-tan, Luster: waxy to dull, Crystal Structure: Microcrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Identified More sedimentary →
Explore Chert (River Pebble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: dull gray to brownish-tan, Luster: waxy to dull, Crystal Structure: Microcrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments; this specimen shows significant smoothing from water transport (fluvial erosion).
Uses & applications
Historically used for stone tools and fire-starting; currently used in construction aggregate and decorative landscaping.
Geological facts
Chert is so hard it can scratch steel; it was the primary material for arrowheads and scrapers during the Stone Age due to its sharp, predictable fracture edges.
Field identification & locations
Identify by its extreme hardness, smooth texture despite lack of visible crystals, and conchoidal (shell-like) fracture patterns if broken. Found globally in riverbeds and gravel pits.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary