Black Jasper

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Black with potential grey or deep blue undertones; Luster: Vitreous to waxy; Crystal structure: Microcrystalline (Trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91.

Formation & Geological History

Formed through the accumulation of silica in sedimentary environments or through the replacement of organic materials or volcanic ash by silica-rich fluids. Often dated back to the Paleozoic or Mesozoic eras depending on the local geology.

Uses & Applications

Used primarily in lapidary work for cabochons, beads, and tumbled stones. Historically used as a 'touchstone' to test the purity of gold and silver.

Geological Facts

Black Jasper, also known as Basanite in certain archaeological contexts, was used by ancient metallurgists to determine the gold content of alloys by the color of the streak left on the stone's surface.

Field Identification & Locations

Identify by its high hardness (won't be scratched by a steel knife) and its smooth, waxy texture when polished. Found commonly in areas with high silica activity, such as riverbeds or coastal regions in India, Egypt, and the USA.

Identified on: 4/16/2026

Mode: Standard