sedimentary
Flint (variety of Chert)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: typically dark grey, black, or deep brown; Luster: waxy to vitreous; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture with sharp edges; Specific gravity: approx 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically dark grey, black, or deep brown
- Luster
- waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: typically dark grey, black, or deep brown; Luster: waxy to vitreous; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture with sharp edges; Specific gravity: approx 2.65.
Formation & geological history
Formed as nodules or masses in sedimentary rocks like chalk and limestone. It is a biochemical precipitate resulting from the replacement of calcium carbonate by silica-rich fluids, often derived from the remains of diatoms or sponges. Common in strata ranging from the Jurassic to the Cretaceous periods.
Uses & applications
Historically used for stone tools (axes, scrapers) and arrowheads; used in 'flintlock' firearms to create sparks. Modern uses include construction aggregate, road surfacing, ceramics, and as decorative landscape stones.
Geological facts
Flint was one of the first materials used by early humans to create fire and weapons. It possesses the unique ability to strike sparks against steel and produces razor-sharp edges when fractured properly (knapping).
Field identification & locations
Identify in the field by its dark color, waxy surface, and characteristic shell-like (conchoidal) fracture patterns when broken. Commonly found in coastal areas, riverbeds flowing through chalk outcrops, and historical quarry sites.
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