sedimentary
Yellow Chert (Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dull yellow to tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Dull yellow to tan
- Luster
- Waxy to vitreous
Identified More sedimentary →
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Physical properties
Hardness: 7 Mohs scale; Color: Dull yellow to tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed primarily in sedimentary environments through the accumulation of silica-rich fluids replacing organic material or through precipitation in marine limestone. Often found as stream-rounded river rocks.
Uses & applications
Historically used for stone tools and weapons due to its sharp conchoidal fracture. Modern uses include tumbling for gravel, craft jewelry, and as a collector's specimen.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create arrowheads and scrapers. Its ability to create sparks when struck against steel made it essential for flintlock mechanisms and fire-starting.
Field identification & locations
Identified in the field by its hardness (cannot be scratched by a steel pocketknife), waxy texture, and half-moon shaped (conchoidal) fractures. Often shows 'impact pits' or chatter marks when found in riverbeds.
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