sedimentary
Chert (Quartz Variety)
Microcrystalline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: Cream, light gray, with yellowish tints; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Cream, light gray, with yellowish tints
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Cream, light gray, with yellowish tints; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. This specimen appears as an eroded river pebble, often dating from the Paleozoic to Mesozoic eras depending on the local strata.
Uses & applications
Historically used for stone tools/arrowheads due to its sharp edges when fractured. Modern uses include construction aggregate, landscaping, and as a low-cost gemstone (tumbled stones).
Geological facts
Chert is so durable that it often remains in riverbeds long after the surrounding limestone or shale has weathered away. High-quality colorful varieties are often referred to as Jasper.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its curved, shell-like (conchoidal) fracture patterns. Commonly found in riverbeds, gravel pits, and coastal areas.
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