sedimentary
Chert with Quartz Vein
Silicon dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Dark brown/black with a cream/tan vein; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture)
- Hardness
- 7 (Mohs scale)
- Color
- Dark brown/black with a cream/tan vein
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Dark brown/black with a cream/tan vein; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; the vein formed later by hydrothermal fluids filling a fracture.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for decorative pebbles and lapidary practice.
Geological facts
Dark varieties of chert are often called flint. The light-colored line is a 'wishing stone' feature, formed when a different mineral fills a crack in the host rock.
Field identification & locations
Identify by its extreme hardness (scratches glass) and smooth, water-worn texture. Common on beaches and in riverbeds globally.
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