sedimentary

Chert (Jasper type)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Brown, reddish-brown, often mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Brown, reddish-brown, often mottled
Luster: Waxy to dull

Identified June 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation from fluids within sedimentary host rocks. Common in ancient marine environments or as nodules in limestone/chalk.

Uses & applications

Historically used for stone tools and arrowheads; currently used as decorative gravel, in lapidary work (cabochons), and as sandpaper abrasive.

Geological facts

Chert is so hard it can create sparks when struck against steel, which made it essential for early flintlock firearms. This specific specimen appears to be water-worn or stream-tumbled.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial tills, and outcrops of sedimentary rock layers.