sedimentary
Chert (with Quartz Veining)
Chert (formula: SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Brownish-gray with white quartz veins. Luster: Dull to waxy. Crystal Structure: Microcrystalline/cryptocrystalline (concealed). Cleavage: None, exhibits conchoidal (shell-like) fracture.
- Hardness
- 6
- Color
- Brownish-gray with white quartz veins
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Brownish-gray with white quartz veins. Luster: Dull to waxy. Crystal Structure: Microcrystalline/cryptocrystalline (concealed). Cleavage: None, exhibits conchoidal (shell-like) fracture.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary layers. The white vein suggests later tectonic stress where silica-rich fluids filled cracks.
Uses & applications
Historically used for stone tools (arrowheads). Today used in road masonry, as decorative gravel, and occasionally for lapidary work if highly colorful.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its use in 'flintlock' firearms. It is one of the most durable and persistent rocks in the geological record.
Field identification & locations
Identify by its hardness (scratches glass), waxy texture on fresh breaks, and conchoidal fracture. Commonly found in riverbeds, glacial till, and embedded in limestone cliffs.
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