sedimentary
Chert (Jasper/Agate variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Multi-colored (red, brown, grey, yellowish); Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Multi-colored (red, brown, grey, yellowish)
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Multi-colored (red, brown, grey, yellowish); 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 silica-rich microfossils or precipitation from silica-saturated waters in sedimentary environments. Can be found in various geological ages from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (knapping); currently used for lapidary work, jewelry (cabochons), and decorative landscaping stones.
Geological facts
Because of its conchoidal fracture, it was the primary material used by prehistoric humans to create arrowheads, spear points, and scrapers.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy appearance, and smooth, shell-like (conchoidal) fractures. Common in river beds, gravel deposits, and limestone formations.
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