sedimentary
Chert (specifically Green Chert/Jasper)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 Mohs; Color: Dark green to dull teal; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 Mohs
- Color
- Dark green to dull teal
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 Mohs; Color: Dark green to dull teal; Luster: Waxy to vitreous; 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 radiolarians) or chemical precipitation from hydrothermal fluids in marine environments. Primarily Paleozoic to Mesozoic era formations.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; modernly used in jewelry (cabochons), as an abrasive, and by collectors for decorative value.
Geological facts
Chert was one of the most important minerals for early humans, used for spearheads and scrapers. The green color in this specimen is typically caused by the presence of silicate minerals like chlorite or iron inclusions.
Field identification & locations
Identify in the field by its smooth, waxy surface and distinct shell-like (conchoidal) fracture patterns. It is harder than steel and will scratch a glass plate. Commonly found in limestone or chalk beds.
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