sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Tan, brownish-yellow, mustard; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque.
- Hardness
- 6
- Color
- Tan, brownish-yellow, mustard
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tan, brownish-yellow, mustard; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque.
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation in marine environments, later undergoing diagenesis. Common in sedimentary beds or as stream-rolled cobbles.
Uses & applications
Used historically for stone tools (arrowheads) due to sharp fracture edges; currently used for landscaping, tumbled stones, and semi-precious jewelry.
Geological facts
Yellow jasper gets its color from iron oxide (goethite) inclusions. It has been used since antiquity for talismans and was known as a stone of protection in several cultures.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and waxy texture when wet. Found frequently in riverbeds and on beaches as water-worn pebbles.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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