sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Yellowish-brown to mustard yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellowish-brown to mustard yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Yellowish-brown to mustard yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine or groundwater environments. This specific specimen shows signs of heavy water erosion (stream/river tumbling), smoothing its edges over thousands of years.
Uses & applications
Historically used for making stone tools (arrowheads/knives) due to its conchoidal fracture. Modernly used for landscaping, as lapidary material for tumbled stones/jewelry, and as an industrial abrasive.
Geological facts
Chert is so durable it often survives long after the surrounding rock has weathered away. High-quality yellow chert is often referred to as 'Yellow Jasper' in the gem trade, even though they are geologically the same material.
Field identification & locations
Identify in the field by its smooth, waxy feel and rounded shape when found in riverbeds; it cannot be scratched by a steel knife. Common in gravel deposits, limestone formations, and coastal areas worldwide.
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