sedimentary

Chert (Jasper/Common Chert)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Brown, tan, reddish-yellow (iron stained); Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Brown, tan, reddish-yellow (iron stained)
Luster: Dull to waxy

Identified May 30, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Brown, tan, reddish-yellow (iron stained); 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 organisms (like radiolaria or diatoms) or by chemical precipitation from groundwater within sedimentary layers. This waterworn pebble likely dates from various geological eras, shaped by fluvial (river) erosion.

Uses & applications

Historically used for making stone tools (arrowheads). Today used in decorative gravel, landscaping, and occasionally as a gemstone when colorful (Jasper).

Geological facts

Chert was one of the first materials used by early humans for fire-starting and hunting tools because it breaks with incredibly sharp edges. It is chemically very resistant to weathering.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), smooth rounded shape if found in rivers, and conchoidal (shell-like) fracture pattern if broken. Commonly found in riverbeds and limestone formations.