sedimentary

Chert (and Jasper variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

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

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, and 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. It often occurs as nodules within limestone or chalk, replacing original carbonate material over millions of years.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp fracture edges. Today it is used in road construction as aggregate, in jewelry (when decorative like jasper), and as a specimen for geological study.

Geological facts

Chert was one of the most important raw materials for early humans because its conchoidal fracture allows it to be shaped into razor-sharp tools. It is highly resistant to chemical weathering.

Field identification & locations

Identify by its waxy luster, smoothness, and 'shell-like' conchoidal fracture patterns. It will scratch glass and won't react with acid. Commonly found in limestone outcrops or as river-worn pebbles.