sedimentary
Chert (and Flint variant)
Chert (SiO2)
Hardness: 7 on Mohs scale. Color: White, tan, or grey with possible banding. Luster: Dull to waxy. Structure: Microcrystalline quartz (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- White, tan, or grey with possible banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: White, tan, or grey with possible banding. Luster: Dull to waxy. Structure: Microcrystalline quartz (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or sponges) or by chemical precipitation from groundwater within limestone or chalk beds. Most common in Paleozoic and Mesozoic rock layers.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used as road aggregate, in glass manufacturing, and as decorative gravel.
Geological facts
Chert is so hard it can produce sparks when struck against steel. It was one of the most important minerals for prehistoric humans to create arrowheads, spear tips, and scrapers.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture patterns and ability to scratch glass. It is often found as nodules inside limestone cliffs or as rounded pebbles in riverbeds. It feels smooth and 'sharp' on the edges.
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