sedimentary
Chert (White Chert / Flint)
Microcrystalline or Cryptocrystalline Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: White to creamy tan; Luster: Waxy or dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- White to creamy tan
- Luster
- Waxy or dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to creamy tan; Luster: Waxy or dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in limestone/chalk deposits. Can range from Precambrian to Holocene in age.
Uses & applications
Historically used for making stone tools (projectile points/scrapers). Modernly used in road construction, gravel, and occasionally as an abrasive or in decorative landscaping.
Geological facts
Chert breaks with a conchoidal fracture, creating extremely sharp edges. Because of this, it was one of the most important minerals for survival in the Stone Age. When struck against steel, it can create sparks, though 'flint' is the name specifically used for this purpose.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its shell-like (conchoidal) fracture pattern, and its smooth, waxy feel. Often found as nodules within limestone or as bedded deposits.
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