sedimentary
Chert (Jasper/Flint variant)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and grayish-yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Variegated brown, tan, and grayish-yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and grayish-yellow; Luster: Waxy to dull; 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 the chemical precipitation of silica in groundwater. It is often found in nodules or bedded layers within limestone or chalk deposits. Ages range from Precambrian to Cenozoic.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modern use includes landscape stone, gemstone cabochons in jewelry, and road aggregate.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges thinner than a steel scalpel. Native American tribes often traded high-quality chert over hundreds of miles. The colored, opaque varieties are often referred to as 'Jasper'.
Field identification & locations
Identify in the field by its smooth, waxy surface and the way it 'rings' when struck. Look for shell-like (conchoidal) curves where it has broken. Common in riverbeds and limestone outcrops globally.
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