sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7.0 (Mohs scale), Color: Variegated (gray core with yellow/red iron-stained cortex), Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7.0 (Mohs scale), Color: Variegated (gray core with yellow/red iron-stained cortex), Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments; the colors result from oxidation of iron minerals within the silica matrix.
Uses & applications
Historically used for stone tools and arrowheads; currently used in jewelry (cabochons), as an abrasive, and for ornamental rock collections.
Geological facts
This specimen displays a distinct weathering rind or oxidation zone where the iron minerals have reacted with water and air to change color from the gray core to red/yellow.
Field identification & locations
Identified by its extremely smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Commonly found in nodules within limestone or as river-worn pebbles.
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