sedimentary
Chert (containing Iron Oxide)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: White to tan with brown/orange iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- White to tan with brown/orange iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: White to tan with brown/orange iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a semi-precious stone for lapidary work.
Geological facts
Chert was one of the most important minerals for prehistoric humans because its conchoidal fracture produces extremely sharp edges, ideal for cutting tools.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) fracture patterns. Frequently found in sedimentary basins.
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