sedimentary
Chert (Jasper/Agate variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, white, and translucent gray; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan, brown, white, and translucent gray
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, white, and translucent gray; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); 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. This specimen appears to have brecciated or replacement textures common in hydrothermal environments.
Uses & applications
Historically used for stone tools (knapping) due to sharp edges; currently used for lapidary work, cabochons, landscaping, and as a collector's specimen.
Geological facts
Chert was one of the most vital materials for early humans to create arrowheads and scrapers. Some varieties containing fossils are known as 'fossiliferous chert'.
Field identification & locations
Identify by its 'flint-like' waxy appearance and shell-like (conchoidal) fractures. It will easily scratch glass. Found globally in limestone formations and river gravel beds.
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