Polished black stone, likely black obsidian

Black, smooth, highly vitreous luster, apparently opaque, with no visible crystals or cleavage; Mohs hardness about 5–5.5 and specific gravity about 2.3–2.6. The rounded shape indicates tumbling or polishing.

Forms when silica-rich volcanic lava cools so rapidly that crystals cannot grow, typically during relatively young volcanic eruptions from the Quaternary to recent geologic time. Common sources include Mexico, the western United States, Armenia, Iceland, and Japan.

Used for ornaments, cabochons, beads, knife blades, and decorative objects; historically fashioned into exceptionally sharp tools and arrowheads.

Obsidian fractures with distinctive conchoidal surfaces and can produce edges sharper than surgical steel, though it is brittle. Some varieties show snowflake, mahogany, rainbow, or sheen effects.

Likely identification requires a glassy luster, conchoidal fracture, lack of mineral grains, and a nonmagnetic response; a scratch test or refractive examination can distinguish it from black glass or onyx. The photograph alone cannot exclude polished basalt, black jasper, or industrial glass.