Chert (specifically Jasper/Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Brown, tan, reddish-brown; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common throughout all geological ages.

Uses & Applications

Historically used for stone tools (arrowheads). Modernly used in landscaping, road construction, and the gemstone industry when occurring as decorative jasper.

Geological Facts

Chert is so hard it can create sparks when struck against steel, making it a primary fire-starting material for ancient civilizations. It is chemically identical to quartz but has a different internal structure.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks into smooth, curved surfaces (conchoidal fracture). Often found in limestone beds or as rounded stream pebbles.

Identified on: 4/20/2026

Mode: Standard