sedimentary
Chert (specifically Yellow or Brown Chert / Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale). Color: Yellow-brown to tan (due to iron oxide inclusions). Luster: Waxy to dull. Crystal Structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Yellow-brown to tan (due to iron oxide inclusions)
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale). Color: Yellow-brown to tan (due to iron oxide inclusions). Luster: Waxy to dull. Crystal Structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary layers. These specimens can range from Precambrian to Cenozoic in age.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as road aggregate, decorative landscaping, and occasionally lapidary work (cabbing) if it has high silica content and takes a polish.
Geological facts
Chert is so hard it can strike sparks from steel, which is why variants like flint were essential for starting fires and for early firearms. It is incredibly durable and resistant to chemical weathering.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture patterns and ability to scratch glass easily. Look for it in riverbeds or as nodules/layers within limestone. Collectors should look for unique banding or translucency.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone
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