sedimentary
Chert / Chalcedony
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, cream, or beige with waxy luster, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, cream, or beige with waxy luster, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used as a construction aggregate, for landscaping, and occasionally as semi-precious gemstones when colorful (Jasper/Agate).
Geological facts
Chert is so hard it can create sparks when struck against steel. It is one of the most common materials used by prehistoric humans for lithic technology.
Field identification & locations
Identify by its waxy luster, smooth/curved (conchoidal) fracture surfaces, and high hardness (it will scratch glass). Commonly found in limestone or chalk beds as nodules.
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