sedimentary
Chert (Banded)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: White, grey, black, tan with banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- White, grey, black, tan with banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, grey, black, tan with banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolaria) or through chemical precipitation in marine or groundwater environments. Can occur as nodules or bedded deposits.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Currently used for lapidary work, jewelry (when highly colored/banded), and road aggregate.
Geological facts
Chert is so hard it can strike sparks against steel. The banding seen in this specimen often represents different cycles of sediment deposition or chemical impurities during formation.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), smooth waxy feel, and characteristic shell-like (conchoidal) breakage patterns. Common in limestone limestone outcrops.
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