sedimentary
Chert
Chert (SiO2)
Hardness: 7 Mohs scale; Color: Grey, black, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8
- Hardness
- 7 Mohs scale
- Color
- Grey, black, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Grey, black, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms like diatoms or radiolaria, or by chemical precipitation. This specimen shows river-worn rounding.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used in road construction, as decorative landscaping stone, or as an abrasive.
Geological facts
Chert is so hard it can strike sparks from steel. Because of its conchoidal fracture, it can be flaked into incredibly sharp edges.
Field identification & locations
Identify by its hardness (it will scratch glass), its smooth waxy feel, and its rounded, water-worn edges if found in riverbeds. Found globally in limestone and chalk deposits.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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