sedimentary
Chert (Jasper/Agate mix)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and waxy grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brown, tan, and waxy grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and waxy grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich fluids in limestone or volcanic cavities, where the silica precipitate hardens over millions of years. This specimen shows a mix of opaque jasper and translucent agate layers.
Uses & applications
Used historically for stone tools due to its sharp edges; currently used for lapidary work, decorative landscaping, and as collector specimens.
Geological facts
Chert has been used since the Stone Age to make arrowheads and spear points. The waxy, translucent portions in this specimen are technically chalcedony/agate.
Field identification & locations
Identify in the field by its waxy appearance and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds, gravel pits, and sedimentary rock outcrops globally.
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