sedimentary
Chert (with Quartz Vein)
Microcrystalline silica (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and gray with white veining; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and gray with white veining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and gray with white veining; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of siliceous remains of organisms or chemical precipitation from silica-rich fluids in sedimentary basins. The white vein suggests secondary quartz precipitation in a fracture.
Uses & applications
Historically used for making stone tools (arrowheads). Modernly used in landscaping, road construction, and as a collector specimen when featuring interesting patterns.
Geological facts
Chert is so hard it can scratch steel. It is one of the most durable rocks and is often found as rounded cobbles in riverbeds or beaches because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its waxy texture, conchoidal (shell-like) fractures, and its ability to scratch glass. Commonly found in limestone or chalk deposits and along coastlines.
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