sedimentary
Chert (Varietal Agate/Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, reddish-orange with white matrix; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 6
- Color
- Brown, tan, reddish-orange with white matrix
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, reddish-orange with white matrix; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed through the precipitation of silica from groundwater in cavities of other rocks or through the accumulation of siliceous oozes in marine environments. Often found in limestone or volcanic host rocks.
Uses & applications
Used historically for stone tools due to conchoidal fracture; modernly used in jewelry (cabbing), lapidary art, and as decorative landscape stone.
Geological facts
Chert was one of the first materials used by early humans to create arrowheads and scrapers. The reddish varieties are often called Jasper, while translucent banded varieties are Agate.
Field identification & locations
Identify by its hardness (will scratch glass), waxy luster on broken surfaces, and lack of visible crystals. Commonly found in river beds or eroded out of limestone cliffs.
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