sedimentary
Chert (specifically Flint or Common Opal variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, and light gray with iron staining; Lustre: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Cream, tan, and light gray with iron staining
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, and light gray with iron staining; Lustre: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in limestone or chalk beds. Most specimens date from the Phanerozoic eon.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to sharp edges; currently used for road surfacing, jewelry (as jasper or agate variants), and as a high-silica industrial resource.
Geological facts
Because of its conchoidal fracture, it breaks into pieces with edges sharper than a steel scalpel. It was the primary 'technological' material for humanity for over two million years.
Field identification & locations
Identify by its 'shell-like' curved fractures and its ability to scratch glass. It is commonly found as nodules in limestone or as bedded deposits in marine sedimentary layers.
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