sedimentary
Chert / Jasper
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Mottled red, orange, tan, and black due to iron oxides and manganese. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Mottled red, orange, tan, and black due to iron oxides and manganese. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by the chemical precipitation of silica in marine environments. Often found in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (arrowheads and scrapers) due to its sharp edges. Currently used for lapidary work, jewelry (cabochons), and as landscaping rock.
Geological facts
Because of its extreme hardness and conchoidal fracture, it was the primary material for prehistoric 'flint knapping.' The red variety is specifically referred to as Jasper.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found in riverbeds or coastal cliffs where sedimentary layers are exposed.
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