sedimentary
Chert / Flint
Cryptocrystalline Quartz (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Variegated grays, blues, and browns as seen in the specimen; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Variegated grays, blues, and browns as seen in the specimen
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated grays, blues, and browns as seen in the specimen; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds. Formation can span from the Precambrian to recent geological eras.
Uses & applications
Historically used for stone tools and starting fires; currently used as a raw material in ceramics, road construction (aggregate), and occasionally as semi-precious gemstones for lapidary work.
Geological facts
Due to its conchoidal fracture, it breaks into razor-sharp edges, making it the primary material for prehistoric arrowheads and spear points. It is often referred to as 'flint' if it occurs in chalk or high-quality dark nodules.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved (conchoidal) breakage surfaces. It is commonly found in riverbeds or weathered out of sedimentary bedrock. Tips: look for the 'waxy' texture compared to surrounding rock.
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