sedimentary
Chert (variant Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: green-yellow, tan, and brown; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- green-yellow, tan, and brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: green-yellow, tan, and brown; 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 diatoms or radiolarians) or through the chemical replacement of limestone/chalk by silica-rich fluids. Common in sedimentary basins of various geological ages.
Uses & applications
Historically used for stone tools/arrowheads due to its sharp edges; used in construction as aggregate and sometimes in jewelry (Jasper/Agate variants) or as a fire-starter (Flint).
Geological facts
Chert is so hard it can scratch steel. Because it breaks with a conchoidal (shell-like) fracture, it was the primary material used by prehistoric humans to create 'knapped' tools like scrapers and projectile points.
Field identification & locations
Identify by its waxy texture, extreme hardness (wont be scratched by a knife), and smooth, curved fracture surfaces. Found frequently in riverbeds or as nodules within limestone outcrops.
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