sedimentary
Flint Pebble
SiO2 (Microcrystalline Quartz / Chalcedony)
Hardness: 7 on the Mohs scale; Color: Dark brown, grey, or black with a lighter weathered cortex; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony); Fracture: Conchoidal; Specific Gravity: 2.60-2.65
- Hardness
- 7 on the Mohs scale
- Color
- Dark brown, grey, or black with a lighter weathered cortex
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on the Mohs scale; Color: Dark brown, grey, or black with a lighter weathered cortex; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony); Fracture: Conchoidal; Specific Gravity: 2.60-2.65
Formation & geological history
Formed through the chemical precipitation of silica-rich fluids within chalk or limestone formations (diagenesis) during the Cretaceous period, later weathered and rounded by wave action into pebbles along beaches.
Uses & applications
Historically used for prehistoric stone tools (knapping for blades and arrowheads), fire-starting with steel, and early firearms (flintlocks). Currently used in industrial ball mills for grinding and occasionally as decorative landscaping stone.
Geological facts
Flint and chert are fundamentally the same material, but 'flint' typically refers to the dark nodules found specifically in chalk deposits. It was one of the most critical materials for early human technological development due to its sharp conchoidal fracture.
Field identification & locations
Easily identified by its conchoidal fracture, high hardness (scratches glass easily), waxy luster, and smooth, water-worn pebble shape commonly found on chalk-cliff beaches (such as the cliffs of southern England or northern France).
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