sedimentary
Chert (Yellow Jasper/Flint)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Yellow-brown, tan, mustard; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellow-brown, tan, mustard
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Yellow-brown, tan, mustard; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins. It is often found as nodules or layers within limestone or shale. Most specimens date from the Phanerozoic eon.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used in landscaping, jewelry (as jasper), and as flint for spark-making. It has high value for lapidary tumbling.
Geological facts
Yellow chert is often referred to as 'Yellow Jasper' when it is opaque and high quality. It was a primary material for prehistoric humans due to its ability to break into sharp, glass-like edges.
Field identification & locations
Identify by its waxy texture and characteristic shell-like (conchoidal) fractures. It will easily scratch glass. Common in riverbeds and limestone outcrops worldwide.
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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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Shale or Slaty Mudstone
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