sedimentary
Chert (Red Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Dull red to reddish-brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91
- Hardness
- 6
- Color
- Dull red to reddish-brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Dull red to reddish-brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91
Formation & geological history
Formed from the recrystallization of silica-rich fluids or the accumulation of silica-based organic remains (like diatoms or radiolarians) in seafloor sediments. Red coloration is typically due to iron oxide (hematite) inclusions.
Uses & applications
Historically used for stone tools and arrowheads due to sharp edges; currently used for lapidary work, jewelry, and as a collector's specimen.
Geological facts
Chert is one of the most durable sedimentary rocks and was among the first materials used by prehistoric humans to create fire and weaponry.
Field identification & locations
Identify by its waxy luster, hardness (will scratch glass), and distinctive shell-like (conchoidal) fracture pattern. Commonly found in stream beds or as nodules within limestone or dolomite.
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