Chert (Jasper variety)

Physical Properties

Hardness: 6.5-7 on the Mohs scale. Color: Opaque reddish-brown and tan. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary basins. It can be found in layers or nodules within limestone or sandstone.

Uses & Applications

Historically used for stone tools (arrowheads/knives) due to its sharp conchoidal edges. Currently used in aquarium decor, landscaping, lapidary arts (tumbled stones), and as an abrasive in some industrial processes.

Geological Facts

Jasper is a variety of chert that gets its red color from iron inclusions. Because of its hardness and density, it was one of the most important minerals for early humans to create survival tools.

Field Identification & Locations

Identify in the field by its waxy texture and shell-like (conchoidal) fracture patterns when broken. It cannot be scratched by a steel knife. Common in ancient sea beds and river gravels.

Identified on: 4/20/2026

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