Polished black stone egg, probably black obsidian

The specimen appears to be a smooth, polished, opaque-to-slightly translucent black egg-shaped object. Obsidian typically has a vitreous/glassy luster, conchoidal fracture, no cleavage, hardness about 5–5.5 on the Mohs scale, and specific gravity around 2.35–2.60. However, the image is partly obscured and does not show diagnostic fracture surfaces, so black onyx, black jasper, basalt, or a non-geological manufactured object cannot be ruled out visually.

If it is obsidian, it formed when silica-rich volcanic lava cooled rapidly, preventing the growth of visible crystals. Obsidian occurs in relatively young volcanic regions, generally from the Cenozoic to the present, although older examples exist. The egg shape is human-made by cutting, grinding, and polishing.

Commonly sold as a decorative carving, meditation or worry stone, paperweight, and mineral-collecting specimen. Obsidian is also used for ornamental objects and, when exceptionally sharp, experimental surgical blades. Comparable black onyx or jasper eggs are used in jewelry and décor.

Obsidian is technically a mineraloid rather than a crystalline mineral because it lacks an ordered crystal structure. Its most diagnostic natural feature is curved, shell-like conchoidal fracture that can produce extremely sharp edges. A polished black surface alone is not sufficient to distinguish obsidian from black glass, resin, onyx, or jasper.

A likely identification is polished black obsidian, but confirmation requires a clearer photograph and simple tests. Inspect the base or an unpolished edge for glassy conchoidal fracture and subtle translucence; obsidian may show faint gray, brown, or flow banding under strong light. It should not be scratched easily by a steel knife, but it can be scratched by quartz. Check weight and temperature response, and avoid destructive testing because polished specimens can be damaged. Common obsidian sources include Mexico, the western United States, Armenia, Turkey, Iceland, Italy, and Japan.