sedimentary
Chert (Flint)
Microcrystalline Opaline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown with reddish iron staining; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or brown with reddish iron staining
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown with reddish iron staining; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains such as radiolarians or diatoms, or through chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and ignition sources (flint and steel). Currently used as a gemstone (Jasper varieties), in road construction, and as a refractory material.
Geological facts
Because of its conchoidal fracture pattern, it breaks into extremely sharp edges, making it the primary material for prehistoric weapons. Some cherts contain well-preserved microfossils of early life forms.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy feel, and smooth, curved fracture surfaces. Found worldwide, particularly in areas with sedimentary limestone deposits.
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