sedimentary
Chert (Jasper/Common Chert)
Microcrystalline Quartz (SiO2)
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
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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.
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