sedimentary
Chert (Jasper transition)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 (Mohs); Color: Brown, tan, and yellow-ochre; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7
- Hardness
- 6
- Color
- Brown, tan, and yellow-ochre
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 (Mohs); Color: Brown, tan, and yellow-ochre; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen shows significant rounding from fluvial (river) or glacial transport.
Uses & applications
Historically used for stone tools (knapping); modernly used for landscaping, as a gemstone (when colorful), and in construction aggregate.
Geological facts
Chert is so durable that it often survives millions of years of erosion that destroy other rocks. This specific specimen has a 'river-worn' or 'cobble' texture, indicating it was moved by water for a long period.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth waxy feel when wet, and its characteristic curved (conchoidal) breaks. It is ubiquitous in river beds and gravel pits globally.
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