sedimentary
Chert (Yellow/Tan)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan to honey-yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan to honey-yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan to honey-yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary beds. These specimens can range from millions to hundreds of millions of years old.
Uses & applications
Historically used for stone tools/arrowheads. Today used as decorative gravel, in road construction, and as tumbling rough for gemstone hobbyists.
Geological facts
Chert is so durable that it often survives as stream pebbles long after the surrounding rock has eroded away. Because it breaks with a sharp edge, it was the primary material for prehistoric tools.
Field identification & locations
Identify by its waxy luster, hardness (it will scratch glass), and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and limestone outcrops.
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