sedimentary
Chert Nodule
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale); Color: Gray, tan, white with a chalky outer cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white with a chalky outer cortex
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white with a chalky outer cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
Formation & geological history
Formed primarily in marine sedimentary environments (such as limestone or chalk beds) through the replacement of carbonate material by silica-rich fluids. It often accumulates in irregular nodular forms or layers.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Modernly used in construction aggregate, road surfacing, and as a low-cost gemstone (jasper/agate varieties).
Geological facts
Chert is essentially the same material as flint; the term 'flint' is usually reserved for dark gray or black chert found in chalk. It is high in silica and can preserve microfossils perfectly.
Field identification & locations
Identify in the field by its distinct conchoidal (shell-like) fracture, extreme hardness (it will scratch glass), and its frequent occurrence as irregular lumps within softer limestone or chalk outcrops.
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