sedimentary
Chert (with Quartz veins)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Grey-blue with white veins; Luster: Waxy to dull; Texture: Smooth, water-worn; Cleavage: None (conchoidal fracture); Opaque.
- Hardness
- 6
- Color
- Grey-blue with white veins
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Grey-blue with white veins; Luster: Waxy to dull; Texture: Smooth, water-worn; Cleavage: None (conchoidal fracture); Opaque.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) on the ocean floor, which later recrystallized under pressure. The white veins are typically quartz or calcite that filled cracks via hydrothermal fluids.
Uses & applications
Used historically for stone tools due to its sharp edges when broken; currently used as decorative garden stone, in road construction, and as collector river rocks.
Geological facts
Chert is extremely durable and chemically stable, which is why it often survives as rounded pebbles in riverbeds or beaches long after other rocks have eroded.
Field identification & locations
Identify by its hardness (it can scratch glass and steel), waxy texture, and the presence of crisscrossing mineral veins. Common in river deposits and coastal areas worldwide.
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