sedimentary
Chert (Flint)
Chert (Microcrystalline or cryptocrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, or grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Forms primarily through the accumulation of silica-rich organic debris (such as radiolaria or diatoms) or by chemical precipitation in sedimentary environments like deep sea floors or limestone beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative stone, in road construction, and for fire-starting strikers.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It was one of the most important minerals for early human survival, used globally to create tools during the Stone Age.
Field identification & locations
Identified by its extremely hard surface (it can scratch glass), waxy feel, and sharp shell-like (conchoidal) fractures. Found in riverbeds, limestone outcrops, and coastal areas.
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