sedimentary
Chert (Flint)
Chert (Microcrystalline or cryptocrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Black, dark gray, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Black, dark gray, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Black, dark gray, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or chemical precipitation of silica in sedimentary environments. Common in limestone and chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used as flint for fire-starting; modern use in construction aggregates and road surfacing.
Geological facts
Flint is a variety of chert that occurs primarily in chalk or marly limestone. It was the primary material for human technological advancement during the Stone Age because its conchoidal fracture creates edges thinner than a steel scalpel.
Field identification & locations
Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Found often as nodules or layers within sedimentary rock outcrops.
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