sedimentary
Banded Chert with Quartz Veining
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and grey banding with white quartz; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and grey banding with white quartz
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and grey banding with white quartz; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. The white veins represent later secondary quartz precipitation in rock fractures.
Uses & applications
Historically used for stone tools; currently used as decorative gravel, in lapidary work for cabochons, and as a geological collecting specimen.
Geological facts
Chert is so durable that it often survives deep into the sediment cycle, appearing as smooth river or beach pebbles long after the surrounding limestone has eroded away.
Field identification & locations
Identify by its hardness (scratches glass), waxy luster, and conchoidal (shell-like) fracture. Commonly found in riverbeds, glacial till, and coastal areas near sedimentary basins.
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