sedimentary
Chert / River Jasper
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, and cream; Luster: Waxy to sub-vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, and cream
- Luster
- Waxy to sub-vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, and cream; Luster: Waxy to sub-vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary rock layers, often found as nodules or pebbles that have been water-worn over millions of years (commonly Paleozoic to Cenozoic eras).
Uses & applications
Commonly used for lapidary work (tumbling and cabochon making), decorative landscaping, and historically for stone tools due to its sharp edges when broken.
Geological facts
Because of its high hardness and brittle nature, prehistoric humans used this material to create arrowheads and scrapers. It is essentially the same mineral as flint, though 'chert' is the broader geological term.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and rounded, water-worn edges if found in riverbeds. It is common in gravel pits and along shorelines globally.
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