sedimentary
Chert (specifically Red Chert / Jasper nodule)
Silicon dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Red, brown, tan, and cream; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Red, brown, tan, and cream
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Red, brown, tan, and cream; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich fluids within sedimentary host rocks, often replacing carbonate material or precipitating in voids. The specimens are frequently found as nodules in limestone or as river-worn cobbles. Most are Paleozoic to Mesozoic in age.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modern uses include decorative landscaping, lapidary work (cabochons), and as a gemstone (Jasper).
Geological facts
Red chert gets its distinctive color from iron oxide inclusions (hematite). It was one of the first materials used by prehistoric humans to create arrowheads and scrapers because it fractures like glass.
Field identification & locations
Identify by its 'flint-like' shell (cortex) on the outside and a waxy, smooth, often colorful interior. Commonly found in riverbeds, glacial tills, and limestone quarries. It will scratch glass and produces a spark when struck with steel.
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