sedimentary

Chert (specifically Brown Chert or Jasper)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 on Mohs scale; Color: Dark brown to liver-colored; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.

Hardness: 6
Color: Dark brown to liver-colored
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 on Mohs scale; Color: Dark brown to liver-colored; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.

Formation & geological history

Formed from the accumulation of microscopic silica-rich shells (radiolaria or diatoms) on the seafloor or via chemical replacement of carbonate materials. Occurs in sedimentary beds and as nodules within limestone or chalk.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as landscaping stone, in road construction (aggregate), and occasionally as a semi-precious gemstone (Jasper).

Geological facts

Chert has been used by humans for millions of years. When struck, it breaks with a conchoidal (shell-like) fracture, creating incredibly sharp edges that were essential for prehistoric survival.

Field identification & locations

Identify in the field by its smooth, waxy texture and curved, glass-like fracture surfaces. It commonly occurs as rounded nodules or distinct layers within sedimentary rock outcrops. It is harder than steel and will scratch a knife blade.