sedimentary
Chert (Jasper/Flint variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brownish-tan; Luster: Waxy to sub-vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Brownish-tan
- Luster
- Waxy to sub-vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Brownish-tan; Luster: Waxy to sub-vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids in sedimentary basins. Often found in nodules or bedded layers.
Uses & applications
Historically used for stone tools/weapons (knapping) due to its sharp edges. Currently used as an abrasive, in landscaping, and as a semi-precious gemstone in jewelry.
Geological facts
Chert is so hard it can strike sparks against steel. It has been used by humans for over 2 million years to create tools like arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy texture, smooth 'shell-like' (conchoidal) fractures, and its ability to scratch glass easily. Commonly found in limestone or chalk deposits.
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