sedimentary
Chert (Yellow Jasper/Flint)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 (Mohs); Color: Yellow, golden brown, tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellow, golden brown, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Yellow, golden brown, tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments. It typically forms in nodules or layered beds within limestone or chalk.
Uses & applications
Historical use for stone tools (arrowheads/scrapers); modern use in jewelry (as yellow jasper cabochons), landscaping, and as a raw material for concrete/road construction.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a steel scalpel. Yellow varieties are often colored by the presence of goethite or limonite (iron oxides).
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy luster, and shell-like (conchoidal) fracture patterns. It is very common in riverbeds and limestone outcrops globally.
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