Chert (specifically Red Chert or Jasper)

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Deep red to brownish-red due to iron inclusions. Luster: Waxy to vitreous. Crystal Structure: Hexagonal (microcrystalline). Fracture: Conchoidal (shell-like curves).

Formation & Geological History

Forms through the accumulation of silica-rich microfossils (like radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins. Primarily Paleozoic and Mesozoic in many regions.

Uses & Applications

Historically used for making stone tools (arrowheads, scrapers) due to sharp edges when fractured. Modernly used in landscaping, as a gemstone (Jasper), and for fire-starting (flint).

Geological Facts

Chert is so hard it can scratch steel. It is frequently associated with limestone formations. Red versions like this are often called Jasper when used in jewelry decoration.

Field Identification & Locations

Identify in the field by its distinctive conchoidal fracture, waxy feel, and ability to scratch glass. Found in riverbeds, desert pavements, and as nodules in limestone.

Identified on: 5/19/2026

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