sedimentary
Chert (with Quartz Veining)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Variegated grays, browns, and whites; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal (veins); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Variegated grays, browns, and whites
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated grays, browns, and whites; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal (veins); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed as a chemical precipitate or through the replacement of limestone by silica-rich fluids. The quartz veins represent a later secondary event where hydrothermal fluids filled fractures in the parent rock.
Uses & applications
Historically used for stone tools and ignition sources (flint); currently used as road aggregate, architectural stone, and occasionally in lapidary work.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges for hunting and scraping.
Field identification & locations
Identify by its extreme hardness, waxy texture, and conchoidal fracture patterns. Found globally in sedimentary basins, often as nodules or bedded layers. Collectors look for unique banding or color patterns.
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