sedimentary
Chert (often called Flint in this variation)
Silicon dioxide (SiO2) - Microcrystalline quartz
Hardness: 7 (Mohs scale); Color: Gray, tan, white, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains in marine environments. Often found as nodules in limestone or chalk beds. Geological age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to its sharp edges. Modern uses include road surfacing, glass manufacturing, and as a starting material for fire (flint and steel).
Geological facts
Chert was one of the most important minerals for early human survival, used for crafting tools for over 2 million years. It is chemically identical to quartz but has a different internal structure.
Field identification & locations
Identify in the field by its waxy appearance and conchoidal (shell-like) fracture patterns with sharp edges. Commonly found in riverbeds or within limestone outcrops. Collectors look for unique banding or fossils trapped within.
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