sedimentary
Chert (Chalcedony/Agate variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brownish-grey with iron oxide staining; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
- Hardness
- 6
- Color
- Tan, brownish-grey with iron oxide staining
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brownish-grey with iron oxide staining; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
Formation & geological history
Formed via the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in sedimentary environments. Common in marine limestone formations.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for landscaping, jewelry (when polished), and as a lapidary material.
Geological facts
This specimen shows typical 'river-worn' rounding and iron staining. Chert has been used by humans for millions of years to create arrowheads and scrapers because of its predictable break patterns.
Field identification & locations
Identify by its waxy texture, lack of visible crystals, and conchoidal (shell-like) fracturing. Common in riverbeds, gravel pits, and coastal areas throughout the United States and Europe.
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