sedimentary
Chert (Yellow Jasper)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan to mustard yellow; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Tan to mustard yellow
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan to mustard yellow; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from groundwater within sedimentary layers or limestone cavities.
Uses & applications
Historical use for stone tools/flintknapping; modern use in landscaping, lapidary work (tumbling/cabbing), and occasionally as a silica source in glassmaking.
Geological facts
Yellow chert is often referred to as 'Jasper' when it is opaque. It is extremely durable and was highly prizes by prehistoric humans for its sharp edges when fractured.
Field identification & locations
Commonly found in riverbeds, gravel pits, and coastal areas as rounded pebbles. Identify by its smooth texture, hardness (cannot be scratched by steel), and shell-like fracture pattern.
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