sedimentary
Chert (varieties include Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from silica-rich fluids within other sedimentary rocks like limestone. Common in Paleozoic and Mesozoic strata.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used in construction aggregate, road surfacing, and as a raw material for ceramics.
Geological facts
Chert nodule formation often replaces carbonate minerals. It was one of the most vital materials for early humans because its conchoidal fracture produces edges sharper than a steel scalpel.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), smooth waxy feel, and curved 'clamshell' fracture patterns. Often found as nodules or layers within limestone beds.
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