sedimentary
Chert (often called Flint or Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or earthy yellow; Luster: Dull to waxy; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or earthy yellow
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or earthy yellow; Luster: Dull to waxy; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/dolomite. This specimen appears to be a nodular variety common in sedimentary basins throughout geological history.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in jewelry (as jasper), as a flux in glass making, and as a durable road aggregate or gemstone polishing material.
Geological facts
Because of its conchoidal fracture, it breaks into pieces with very sharp edges, leading ancient civilizations to use it for arrowheads and knives. Flint is a specific variety of chert often found in chalk or marly limestone.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), its smooth 'conchoidal' (shell-like) fracture surfaces, and its waxy feel. It is commonly found in riverbeds, agricultural fields, or weathered out of limestone cliffs.
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