sedimentary

Chert (Agatized/Chalcedony variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Tan, brown, white, and waxy grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Tan, brown, white, and waxy grey
Luster: Waxy to dull

Identified May 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Tan, brown, white, and waxy grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. The silica often replaces original limestone or organic material over millions of years.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp conchoidal fracture. Today used for lapidary work, decorative landscaping, and as a source of silica in glass manufacturing.

Geological facts

Chert is so durable that it can survive long periods of erosion and travel great distances in riverbeds. Ancient civilizations prized certain colors of chert for trade across continents.

Field identification & locations

Identify by its waxy luster, extreme hardness (it will scratch glass), and distinctive curved, shell-like (conchoidal) fractures. Often found in limestone outcrops or as rounded river cobbles.