sedimentary
Chert (Yellow Jasper variant)
Microcrystalline quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Ochre yellow to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 6
- Color
- Ochre yellow to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Ochre yellow to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (diatoms/radiolaria) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine limestone and chalk deposits.
Uses & applications
Historically used for stone tools and arrowheads; currently used in lapidary work, jewelry (cabochons), and as aquarium or decorative stones.
Geological facts
Chert has a distinctive conchoidal fracture, allowing it to break with very sharp edges. Humans have used this material for over 2 million years to create tools and spark fires.
Field identification & locations
Identify in the field by its waxy texture, inability to be scratched by a steel blade, and smooth, shell-like (conchoidal) breakage patterns. Often found in riverbeds or eroded out of limestone outcrops.
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