sedimentary
Banded Chert
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: White, cream, gray with alternating bands. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- White, cream, gray with alternating bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: White, cream, gray with alternating bands. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the accumulation of siliceous remains of organisms like diatoms or radiolarians, or via chemical precipitation from silica-rich groundwater. Often found in marine sedimentary layers from various geological periods.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include use in construction aggregates and occasionally for lapidary work or as tumbled pocket stones.
Geological facts
Chert is so hard it can strike sparks against steel, a trait that made it essential for flintlock firearms. The banding represents changes in the depositional environment over time.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy feel, and conchoidal fracture patterns. Commonly found in riverbeds or limestone outcrops.
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