Jasper

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, orange, yellow; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.91

Formation & Geological History

Formed through the infiltration of silica-rich fluids into volcanic ash or fine-grained sediments. Over time, the silica crystallizes into a microcrystalline quartz variety known as jasper. Coloring is typically caused by iron oxides (hematite/goethite) trapped within the silica.

Uses & Applications

Used primarily in lapidary arts for cabochons, beads, and sculpture. In history, it was used for seals and early stone tools due to its toughness and conchoidal fracturing.

Geological Facts

Jasper was a favorite gem in the ancient world; its name can be traced back in Hebrew, Assyrian, Persian, Greek, and Latin. It is an opaque variety of chalcedony.

Field Identification & Locations

Identify in the field by its opacity (even on thin edges), its hardness (it will scratch glass), and its smooth, shell-like fracture surfaces. Often found as river-worn cobbles in areas with volcanic history.

Identified on: 4/24/2026

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