sedimentary
Brown Chert
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Dull brown to reddish-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Dull brown to reddish-brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Dull brown to reddish-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed in sedimentary environments via the accumulation of siliceous remains of organisms (microfossils) or through chemical precipitation from silica-rich fluids within other rock layers.
Uses & applications
Historically used for making stone tools due to its sharp edges; currently used for road ballast, landscaping, and lapidary work.
Geological facts
Chert is essentially the same as flint, though 'flint' is often reserved for specimens found in chalk. It is highly resistant to weathering and is one of the most durable sedimentary rocks.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass and steel), and smooth, shell-like (conchoidal) breakage patterns. Found globally in limestone and dolomite beds.
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