sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2) with iron inclusions
Hardness: 6.5-7 Mohs; Color: Opaque brown, ochre, and red; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque brown, ochre, and red
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Opaque brown, ochre, and red; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich fluids or remains of siliceous organisms (like radiolaria) in sedimentary environments. Iron oxide inclusions provide the brown/red pigmentation.
Uses & applications
Historically used for stone tools (knapping). Currently used for lapidary work, decorative landscaping, and as educational specimens.
Geological facts
Chert and Jasper are chemically the same as quartz but have a microscopic crystalline structure. In ancient times, it was widely used to create sharp edges for arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy appearance, and characteristic curved, shell-like (conchoidal) fractures. Found globally in limestone and dolomite formations.
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