sedimentary
Red Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Red, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91
- Hardness
- 6
- Color
- Red, reddish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Red, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians) or chemical precipitation from hydrothermal fluids in marine environments. Red coloring comes from iron oxide inclusions.
Uses & applications
Used primarily for lapidary work (jewelry, cabochons), ornamental stone, and historically for stone tools due to its sharp conchoidal fracture.
Geological facts
In antiquity, red chert was often used to create spear points and knives because of its extreme hardness and ability to hold a razor-sharp edge. It is a common constituent of 'banded iron formations'.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its inability to be scratched by a steel knife. Commonly found in riverbeds or as nodules in limestone/dolomite.
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