sedimentary
Chert (Jasper)
Sedimentary Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Dull green with orange-brown iron staining; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Dull green with orange-brown iron staining
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Dull green with orange-brown iron staining; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in marine environments. Often found in nodules or bedded layers.
Uses & applications
Used historically for stone tools due to conchoidal fracturing; modernly used in jewelry (as jasper), lapidary arts, and as decorative gravel.
Geological facts
This specimen appears to be a water-worn or tumbled pebble of chert. Chert is one of the most durable sedimentary rocks and can preserve microfossils dating back billions of years.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy feel, and sharp shell-like edges when broken. Commonly found in riverbeds and coastal areas where harder minerals concentrate as softer rock erodes.
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