sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline or Cryptocrystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: typically tan, grey, or green-brown; Luster: waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically tan, grey, or green-brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically tan, grey, or green-brown; Luster: waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like diatoms or radiolarians) within sedimentary beds. This specimen appears weather-worn but shows typical conchoidal scarring.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as a component in construction aggregate, road metal, and sometimes for decorative jewelry when highly colored.
Geological facts
Chert was one of the most important raw materials for early humans; when struck against steel, it produces sparks, leading to its extensive use in flintlock firearms and fire-starting kits.
Field identification & locations
Identify in the field by its hardness (will scratch glass easily) and its characteristic shell-like (conchoidal) fracture patterns when broken. Commonly found in limestone or chalk beds.
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