sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2) with Iron Oxide impurities
Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown, tan, and grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
- Hardness
- 6
- Color
- Reddish-brown, tan, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown, tan, and grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in sedimentary environments. Its reddish color is due to iron oxide inclusions.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include jewelry (lapidary), decorative landscaping, and as a raw material for silica manufacturing.
Geological facts
Red chert is often specifically called Jasper. It was one of the most important materials for prehistoric humans because it breaks with a sharp edge, similar to flint or obsidian.
Field identification & locations
Identify in the field by its hardness (will scratch glass), conchoidal fracture pattern, and waxy texture. It is extremely common in riverbeds and sedimentary outcrops globally.
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