sedimentary
Chert (and Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Typically grey, tan, or white with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Typically grey, tan, or white with distinct banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Typically grey, tan, or white with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or through the chemical precipitation of silica in groundwater. Can be found in rocks from the Precambrian era to the present.
Uses & applications
Used historically for stone tools (arrowheads, scrapers) due to its sharp edges; used today as road base, in concrete, and as high-quality flint for fire-starting. Banded varieties are used as ornamental stones.
Geological facts
Chert is so hard it can scratch steel. It was the primary material for the Stone Age technology. The 'flint' used in flintlock firearms is a variety of dark-colored chert.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture patterns and ability to scratch glass. It is commonly found as nodules in limestone or as distinct bedded layers. Collector tips: look for smooth, waxy surfaces and sharp edges.
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