sedimentary
Chert (Jasper/Flint variety)
Microcrystalline silicon dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, reddish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen shows significant rounding typical of fluvial (river) transport, likely dating from various sedimentary eras.
Uses & applications
Historically used for stone tools and weapons due to its sharp conchoidal fracture. Today used as road gravel, in landscape gardening, and occasionally for lapidary work if it has high color patterns.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms and fire-starting kits.
Field identification & locations
Identify in the field by its waxy texture, lack of visible grains, and shell-like (conchoidal) curved breaks. It is very common in riverbeds and glacial tilt deposits.
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