sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Tan, beige, or grey with a white chalky cortex; Luster: Dull to waxy; Structure: Microcrystalline; Fracture: Conchoidal with sharp edges; Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Tan, beige, or grey with a white chalky cortex
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: Tan, beige, or grey with a white chalky cortex; Luster: Dull to waxy; Structure: Microcrystalline; Fracture: Conchoidal with sharp edges; Specific Gravity: 2.65
Formation & geological history
Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms) within limestone or chalk beds. Often occurs as nodules or beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in construction aggregate and as a collector's specimen for demonstrating conchoidal fracture.
Geological facts
Flint is a variety of chert that occurs specifically in chalk or marly limestone. It has been used by humans for over two million years and was the primary material for the Stone Age technology revolution.
Field identification & locations
Identify by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Often found as nodules with a white, weathered outer layer in sedimentary basins.
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