sedimentary
Chert (Yellow or Tan Chert)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (can scratch steel); Color: Tan, yellow, or mustard brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Tan, yellow, or mustard brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (can scratch steel); Color: Tan, yellow, or mustard brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the accumulation of siliceous remains of organisms like diatoms or radiolarians, or by chemical precipitation of silica-rich fluids. Often found in nodules, beds, or vein deposits within limestone or chalk formations.
Uses & applications
Historically used for stone tools due to its sharp edges when broken. Today used in construction as aggregate, in high-end lapidary work, and for primitive fire-starting (as flint).
Geological facts
Chert is chemically identical to quartz but contains impurities that give it opaque colors. Flint is a dark variety of chert. This specific specimen may have been modified by humans into a flake or lithic debitage.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture patterns and the fact that it is too hard to be scratched by a steel nail. Commonly found in riverbeds and limestone outcrops.
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