sedimentary
Chert (often called Flint when dark)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, green, or black with waxy luster; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, green, or black with waxy luster
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, green, or black with waxy luster; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation in marine environments and limestone beds. Prevalent in Paleozoic to Mesozoic strata.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road surfacing, fire-starting kits (flint and steel), and as a gemstone when colorful (Jasper).
Geological facts
Because of its conchoidal fracture, it breaks into razor-sharp edges, making it the most important material for prehistoric humans to create survival tools.
Field identification & locations
Identify in the field by its very smooth, waxy surface and curved, glass-like fracture (conchoidal). It is extremely hard and will scratch glass easily.
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