sedimentary
Chert (specifically Brown Chert or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, or yellowish-brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.65.
- Hardness
- 6
- Color
- Brown, tan, or yellowish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, or yellowish-brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. It is often found as nodules or layers within limestone or carbonate rocks.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as road aggregate, in landscaping, and as a semi-precious gemstone when polished.
Geological facts
Chert is extremely durable and weather-resistant. It was one of the most important minerals for early humans because of its ability to produce sharp edges when fractured.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and distinctive shell-like (conchoidal) fracture pattern. Commonly found in riverbeds and sedimentary outcrops.
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