sedimentary
Chert / Flint
Microcrystalline or cryptocrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark brown to black; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dark brown to black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown to black; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from seawater or hydrothermal fluids, often replacing other minerals or organic matter within limestone or chalk formations. These processes occur over millions of years.
Uses & applications
Historically used for making stone tools and starting fires; currently used in construction as an aggregate, in road surfacing, and occasionally for jewelry as a semi-precious stone.
Geological facts
Flint is a variety of chert used by prehistoric humans to create sharp edges for arrowheads and knives. It produces sparks when struck against steel, making it vital for early fire-making and flintlock firearms.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found as nodules in limestone or as pebbles in riverbeds and on beaches.
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