sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dull yellow to brownish with iron oxide streaks; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 Mohs scale
- Color
- Dull yellow to brownish with iron oxide streaks
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Dull yellow to brownish with iron oxide streaks; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation in marine or groundwater environments. It is a dense, hard sedimentary rock often found in nodules or bedded layers.
Uses & applications
Used historically for stone tools due to its sharp edges when fractured. Currently used for lapidary work, jewelry (tumbled stones), and as an abrasive or decorative landscaping material.
Geological facts
Yellow jasper is specifically chert colored by goethite or other iron oxides. It has been used by humans for hundreds of thousands of years to create projectile points and scrapers.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy feel, and characteristic conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or coastal areas.
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Brecciated Chert (Microcrystalline Silica)
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