sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Yellow, tan, brownish-yellow; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Yellow, tan, brownish-yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Yellow, tan, brownish-yellow; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (flintknapping) due to sharp edges; currently used for lapidary work, jewelry, and as a decorative landscaping stone.
Geological facts
Yellow jasper is a variety of chert that gets its color from iron oxide (goethite or limonite) inclusions. It has been used by humans for millions of years to create scrapers and arrowheads.
Field identification & locations
Identify in the field by its smooth, waxy surface and its ability to scratch glass. Look for curved, shell-like (conchoidal) fractures on broken edges. Common in riverbeds and sedimentary outcrops.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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