Chert (Jasper/Flint variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored (tan, grey, black, brown); Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids. Occurs commonly in sedimentary beds as nodules or bedded deposits.

Uses & Applications

Historically used for stone tools and weapons (arrowheads) due to its sharp conchoidal edges; currently used in jewelry (as jasper), landscaping, and as a component in aggregate production.

Geological Facts

Chert is so hard that it can strike sparks from steel, which led to its historically vital use in 'flintlock' firearms. It is incredibly durable and resistant to chemical weathering.

Field Identification & Locations

Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Common in limestone regions and as river-worn cobbles. Collectors look for unique banding or color patterns.

Identified on: 4/27/2026

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