sedimentary
Chert (Flint)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, and grey; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, and grey; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the precipitation of microcrystalline silica from water, often as nodules or layers within limestone or chalk beds. This specimen likely dates from the Mesozoic or Cenozoic era.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Industrially used as an abrasive and in various construction aggregates. Popular among collectors as tumbling rough.
Geological facts
Flint is a specific variety of chert. When struck against steel, flint produces sparks, making it essential for ancient survival and early firearms (flintlocks).
Field identification & locations
Identifiable by its sharp, curved (conchoidal) edges and waxy texture. Commonly found in riverbeds, chalk cliffs, and fields over limestone bedrock.
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