sedimentary
Chert (Jasper variation)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brownish-tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; age can range from Precambrian to Holocene.
Uses & applications
Historically used for making stone tools (arrowheads); currently used as abrasive media, road surfacing, or decorative landscape stone.
Geological facts
Chert is so hard it can strike sparks against steel, which made it vital for flintlock firearms; it is essentially a non-banded form of chalcedony.
Field identification & locations
Identify by its extreme hardness (scratches glass) and smooth, shell-like (conchoidal) fracture surfaces; found globally in limestone and chalk beds.
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