sedimentary
Chert (specifically Red Chert/Jasper nodule)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Red, maroon, and white banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Red, maroon, and white banding
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Red, maroon, and white banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in sedimentary environments. The red color is caused by iron oxide inclusions.
Uses & applications
Used historically for stone tools (arrowheads/scrapers) due to conchoidal fracturing. Modern uses include decorative landscaping, lapidary work (cabochons), and as an industrial abrasive.
Geological facts
Red chert is often termed 'Jasper' when it is opaque. It was one of the most vital materials for prehistoric humans because it can be knapped into extremely sharp edges.
Field identification & locations
Identify in the field by its smooth, waxy surface and sharp, curved (conchoidal) edges where broken. It is harder than steel and will scratch glass. Commonly found in riverbeds or limestone deposits.
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