igneous
Golden Sheen Obsidian
Volcanic Glass (predominantly SiO2, >70%)
AI-generated identification · may be incorrectMohs hardness: 5.0 - 5.5; Color: Jet black body with a shimmering golden or bronze optical iridescence/sheen under directional light; Luster: Vitreous to sub-metallic sheen; Cleavage: None (conchoidal fracture); Crystal structure: Amorphous (mineraloid); Specific gravity: ~2.35 - 2.60.
- Hardness
- 5
- Luster
- Vitreous to sub-metallic sheen
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Physical properties
Mohs hardness: 5.0 - 5.5; Color: Jet black body with a shimmering golden or bronze optical iridescence/sheen under directional light; Luster: Vitreous to sub-metallic sheen; Cleavage: None (conchoidal fracture); Crystal structure: Amorphous (mineraloid); Specific gravity: ~2.35 - 2.60.
Formation & geological history
Formed through the rapid cooling and solidification of highly felsic (silica-rich) rhyolitic lava, preventing mineral crystallization. The distinctive golden sheen is caused by microscopic, aligned gas bubbles and micro-crystallite inclusions trapped along flow planes during volcanic extrusion.
Uses & applications
Commonly carved and polished into decorative objects (such as eggs, spheres, and cabochons), beads, and jewelry. Historically used for extremely sharp cutting tools, blades, and ritual mirrors.
Geological facts
Obsidian fractures conchoidally to an edge that can be much sharper than modern surgical steel scalpels (often only a few molecules thick). The golden sheen effect appears dynamically as the specimen is rotated under a light source, creating a 'cat's eye' or chatoyant flash.
Field identification & locations
Recognized in the field by its glassy texture, shell-like (conchoidal) fractures, sharp edges, and unique metallic/golden flash under sunlight. Prominent sources include Jalisco and Hidalgo (Mexico), the western United States (Oregon, California), and Armenia.
