sedimentary

Chert (and Limestone) River Cobble

Microcrystalline Quartz (SiO2) within Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (mohs); Color: Grey-blue with white/buff veining; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Grey-blue with white/buff veining
Luster: Dull to waxy

Identified March 22, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (mohs); Color: Grey-blue with white/buff veining; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments duringvarious geological periods (frequently Paleozoic). This specific specimen shows rounding from water transport in a river or glacial environment.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for garden landscaping, road aggregate, and as a decorative river rock.

Geological facts

Chert is so durable it often survives millions of years of erosion that destroys surrounding rocks. It was the primary material for flintknapping arrowheads and tools by prehistoric humans.

Field identification & locations

Identify by its 'slick' feel compared to other stones and its ability to scratch glass. Commonly found in riverbeds, glacial tills, and coastal beaches. Look for conchoidal (shell-like) chips on the surface.