sedimentary
Chert (Jasper/Agate variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, reddish-orange; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brown, tan, reddish-orange
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, reddish-orange; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the accumulation of silica-rich micro-organic remains or chemical precipitation from hydrothermal fluids in sedimentary basins. This specimen appears water-worn.
Uses & applications
Historically used for stone tools/arrowheads; currently used as decorative gravel, in lapidary work (tumbling/polishing), and for jewelry-making.
Geological facts
Chert is so durable that it can survive long-distance transport in rivers and glacial deposits, often outlasting the softer rocks it was originally embedded in.
Field identification & locations
Identify in the field by its waxy texture, extreme hardness (it will scratch glass), and its smooth, shell-like fracture pattern when broken. Commonly found in riverbeds and gravel pits.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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