sedimentary

Chert (or Microcrystalline Quartz)

Chert (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, or off-white
Luster: Dull to waxy

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in saltwater environments. Often found as nodules within limestone or shale beds.

Uses & applications

Historically used for making stone tools due to its conchoidal fracture (sharp edges). Modern uses include construction aggregate, road surfacing, and decorative landscaping rock.

Geological facts

Chert is so hard it can strike sparks against steel, a property that led to its use in flintlock firearms. 'Flint' is actually just a dark-colored variety of chert.

Field identification & locations

Look for a smooth, waxy texture and edges that break like thick glass (conchoidal fracture). It is frequently found in riverbeds or eroded out of limestone cliffs. Collectors value 'omars' or specifically shaped nodules.