sedimentary
Chert (specifically Banded Chert or Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, white, and reddish-brown bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, white, and reddish-brown bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, white, and reddish-brown bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or chemical precipitation from silica-rich fluids in limestone or chalk beds. This specific specimen shows iron oxide staining resulting in the reddish stripes.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modernly used in landscaping, road construction, and as a semi-precious stone for lapidary work.
Geological facts
Chert was one of the most important minerals for early humans, used to create arrowheads and scrapers. When struck against steel, it can produce sparks, leading to its frequent use in flintlock firearms.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fracture patterns. It will easily scratch glass. Commonly found in stream beds or weathered out of carbonate rock outcrops.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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