sedimentary
Chert (variously known as Flint or Jasper)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 on the Mohs scale; Color: Gray, tan, or brown (often with white veins); Luster: Waxy to dull; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (exhibits conchoidal fracture); Specific Gravity: 2.6 – 2.7
- Hardness
- 7 on the Mohs scale
- Color
- Gray, tan, or brown (often with white veins)
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on the Mohs scale; Color: Gray, tan, or brown (often with white veins); Luster: Waxy to dull; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (exhibits conchoidal fracture); Specific Gravity: 2.6 – 2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical replacement of limestone/chalk by silica-rich fluids. It occurs as nodules or layers within sedimentary beds and can range from Precambrian to modern ages.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to its sharp edges; used today as a construction aggregate, for road surfacing, and occasionally in jewelry as polished stones.
Geological facts
Chert was one of the most important raw materials for early humans because of its predictable 'conchoidal' fracturing patterns, allowing it to be Worked into tools. It is also famous for preserving very old microfossils.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved 'shell-like' fractures. Commonly found in riverbeds or within limestone outcrops. Collectors look for unique banding or color patterns.
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