sedimentary

Chert (or Chalcedony) Nodule

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Tan, beige, or yellowish-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Tan, beige, or yellowish-brown
Luster: Dull to waxy

Identified July 16, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, beige, or yellowish-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed in sedimentary environments, often replacing carbonate material or precipitating from silica-rich fluids within limestone or chalk beds. Commonly found in Paleozoic or Mesozoic age strata.

Uses & applications

Historically used for stone tools due to sharp edges; currently used for road base, decorative landscaping, and occasionally lapidary art if high quality.

Geological facts

This specimen appears to be a weathered chert nodule, likely tumbled by water. Chert is so durable that it often remains long after the surrounding limestone host rock has eroded away.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy texture when broken, and lack of reaction to acid. Often found in riverbeds or gravel pits.