sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Tan, brown, and grey; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Tan, brown, and grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 Mohs; Color: Tan, brown, and grey; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed in marine environments via the accumulation of siliceous remains from organisms like diatoms and radiolarians, or through chemical precipitation in limestone/chalk beds. Dates from Precambrian to recent.
Uses & applications
Historically used for stone tools (arrowheads, knives) and striking fire; currently used as a decorative stone, in jewelry (lapidary), and as a surfacing material for roads.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. Because of its conchoidal fracture, it can be knapped into extremely sharp edges, some thinner than a steel scalpel.
Field identification & locations
Identify by its hardness (scratches glass), waxy feel, and characteristic shell-like (conchoidal) fractures. Common in sedimentary basins worldwide.
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