sedimentary
Chert (specifically Tan/Brown Chert)
Chert (SiO2)
Hardness: 7.0 on Mohs scale; Color: Tan, beige, or light brown; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline (cannot see crystals with naked eye); Cleavage: None (exhibits characteristic conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7
- Color
- Tan, beige, or light brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7.0 on Mohs scale; Color: Tan, beige, or light brown; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline (cannot see crystals with naked eye); Cleavage: None (exhibits characteristic conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or via chemical precipitation in marine or groundwater environments. This particular specimen appears to be 'nodular' chert, often found within limestone and dolomite formations of various geological ages from the Precambrian to present.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal edges; currently used as a flux in smelting, for glass manufacturing, as road ballast, and for 'flint' in spark-striking mechanisms.
Geological facts
Because it breaks with a smooth, curved 'conchoidal' fracture similar to glass, it was one of the most important minerals for early humans in the production of weapons and tools. When struck with steel, it produces sparks, leading to its frequent confusion with Flint (a dark variety of chert).
Field identification & locations
Identify in the field by its hardness (it will easily scratch steel or glass) and its smooth, shell-like fracture surfaces. It feels much smoother and colder than surrounding sandstone or limestone. It is found globally in sedimentary basins. For collectors, look for creek beds or limestone outcroppings.
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