Red Jasper (possibly Chert/Argillite)

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Deep reddish-brown to terracotta. Luster: Dull to waxy when unpolished. Crystal structure: Microcrystalline (trigonal). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58–2.91.

Formation & Geological History

Formed through the deposition of silica from hydrothermal fluids or in sedimentary environments where volcanic ash or fine-grained sediments are silicified. The red color is derived from high levels of iron oxide (hematite).

Uses & Applications

Used primarily in lapidary work for jewelry, cabochons, and decorative carvings. Historically used for making stone tools (scrapers, arrowheads) due to its durability and sharp edges when fractured.

Geological Facts

Jasper has been a favorite gemstone since antiquity; it is mentioned in Babylonian and Hebrew texts and was frequently used in the ancient world for cylinder seals and amulets. It is often found as river-worn cobbles.

Field Identification & Locations

Identify in the field by its opaque nature (it does not pass light even on thin edges), its smooth conchoidal fracture, and inability to be scratched by a steel knife. Commonly found in riverbeds and along coastlines in volcanic or sedimentary regions.

Identified on: 4/26/2026

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