sedimentary
Red Chert (Jasper)
Cryptocrystalline Quartz (SiO2) with iron oxide inclusions
Hardness: 6.5-7 Mohs; Color: Brick red to brownish-red; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brick red to brownish-red
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brick red to brownish-red; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed in marine environments where silica-rich fluids replace organic matter or precipitate from hydrothermal solutions, often found in nodules or bedded deposits within limestone or dolomite.
Uses & applications
Used historically for stone tools due to its sharp edges; modernly used as decorative gravel, in lapidary work for cabochons and jewelry, and as a gemstone (Jasper).
Geological facts
Red chert is often called jasper when it is opaque and highly polished. It has a distinctive 'flint-like' fracture pattern that made it a favorite for arrowheads and scrapers among ancient civilizations.
Field identification & locations
Identify in the field by its hardness (scratches glass), opaque appearance, and smooth, shell-like (conchoidal) breaking surfaces. Commonly found in riverbeds, glacial deposits, and sedimentary outcrops worldwide.
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