sedimentary
Chert
Microcrystalline Quartz (SiO2) with iron oxide staining
Hardness: 7 Mohs; Color: Brownish-yellow, tan, honey-colored; Luster: Waxy to sub-vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 Mohs
- Color
- Brownish-yellow, tan, honey-colored
- Luster
- Waxy to sub-vitreous
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Physical properties
Hardness: 7 Mohs; Color: Brownish-yellow, tan, honey-colored; Luster: Waxy to sub-vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids within sedimentary environments, often replacing limestone or forming nodules in oceanic and lake beds. This specimen exhibits iron staining resulting from weathering.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracture. Modernly used in landscaping, road construction, and occasionally for flint-striking fire starters.
Geological facts
Chert has been used by humans for hundreds of thousands of years. When struck, it breaks into pieces with very sharp edges. It is one of the toughest and most weather-resistant common rocks.
Field identification & locations
Identify by its high hardness (it will scratch glass), waxy luster when wet or polished, and the characteristic curved (conchoidal) breaks. Often found as nodules within limestone or as river pebbles.
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