sedimentary
Chert (Flint)
Microcrystalline Quartz or Cryptocrystalline Silica (SiO2)
Hardness: 7 (Mohs scale). Color: Tan, brown, and grey. Luster: Waxy to dull. Crystal Structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale). Color: Tan, brown, and grey. Luster: Waxy to dull. Crystal Structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments like limestone beds. Common in various geological ages ranging from Precambrian to recent strata.
Uses & applications
Historically used for stone tools and fire-starting. Currently used as an aggregate in road construction, landscaping, and as decor for collectors.
Geological facts
Chert has been used by humans for hundreds of thousands of years to craft arrowheads and knives because of its sharp conchoidal fracture edges.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (scratches glass), and the way it breaks into smooth, curved surfaces (conchoidal fracture). Commonly found in nodular forms within limestone.
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Brecciated Chert (Microcrystalline Silica)
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