sedimentary
Chert (Yellow Jasper variant)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Yellow to tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellow to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Yellow to tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/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 or groundwater environments. Can vary in age from Precambrian to Cenozoic.
Uses & applications
Historically used for making stone tools (arrowheads); currently used for decorative gravel, landscaping, and as a semi-precious gemstone for jewelry when polished.
Geological facts
Chert is so hard it can create sparks when struck against steel. Yellow Jasper specifically gets its color from iron oxide inclusions and is often found in riverbeds as water-worn pebbles.
Field identification & locations
Identify in the field by its waxy texture and shell-like (conchoidal) fractures. Common in sedimentary basins and river gravels. Collectors look for smooth, color-saturated pieces for tumbling.
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