sedimentary

Chert / Chalcedony

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified June 5, 2026More sedimentary →

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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.