sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Opaque yellow, tan, and brown. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque yellow, tan, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Opaque yellow, tan, and brown. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids in sedimentary environments or through the replacement of limestone. This specimen likely originated from hydrothermal activity or secondary silica deposition in cracks.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Modern uses include jewelry (cabochons), landscaping decorative stone, and as a collector's specimen.
Geological facts
Chert is so durable that it often survives as stream gravel long after the surrounding rock has weathered away. Early humans transitioned from using basic stones to chert and flint because of their predictable fracture patterns.
Field identification & locations
Identify in the field by its waxy luster, extreme hardness (it will scratch glass), and shell-like (conchoidal) fractures. Often found in riverbeds or within limestone outcrops.
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