sedimentary
Chert (Jasper)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Mottled brown, tan, and grey with possible iron oxide staining. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Mottled brown, tan, and grey with possible iron oxide staining. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the precipitation of silica-rich fluids or from the accumulation of silica-based micro-organic remains (like radiolarians) on the ocean floor. Commonly Paleozoic to Mesozoic in age.
Uses & applications
Historically used for stone tools (arrowheads). Today used in jewelry, lapidary arts as 'river jasper', and occasionally as aggregate in road construction.
Geological facts
Chert and Jasper are essentially the same material; the name Jasper is typically applied to opaque, colorful, or patterned varieties used as gemstones.
Field identification & locations
Identify in the field by its smooth texture, conchoidal fracture (curved breaks), and hardness (cannot be scratched by a steel knife). Commonly found in riverbeds and limestone formations.
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