sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, and white; Luster: Waxy to dull; Structure: Cryptocrystalline with angular clasts; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, and white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, and white; Luster: Waxy to dull; Structure: Cryptocrystalline with angular clasts; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the fragmentation of chert (a microcrystalline sedimentary rock) followed by cementation, often by silica-rich fluids. The angular nature of the pieces suggests they were broken by tectonic forces or collapse and cemented in place without significant transport.
Uses & applications
Primarily used for geological study, landscaping, and aggregate. Historically, chert was used for tool making (flint knapping), though brecciated forms are less ideal due to internal fractures.
Geological facts
The angular 'fragments' visible in the rock are called clasts. This specific specimen shows 'sedimentary breccia' characteristics, often indicating ancient fault zones or karst collapse environments.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and the visible pattern of broken, angular fragments cemented together. Frequently found in riverbeds or near limestone outcrops.
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