igneous
Likely obsidian (possibly tektite or slag glass)
Volcanic glass; primarily SiO₂, noncrystalline
AI-generated identification · may be incorrectDark blue-black, vitreous luster, conchoidal-looking fractures, no visible crystals or cleavage; Mohs hardness about 5–5.5, specific gravity about 2.35–2.65. The rounded, irregular form may indicate natural weathering or human tumbling.
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Physical properties
Dark blue-black, vitreous luster, conchoidal-looking fractures, no visible crystals or cleavage; Mohs hardness about 5–5.5, specific gravity about 2.35–2.65. The rounded, irregular form may indicate natural weathering or human tumbling.
Formation & geological history
Obsidian forms when silica-rich lava cools so rapidly that crystals cannot grow, typically during volcanic eruptions in the Cenozoic or older volcanic episodes. The strong blue color could also reflect uncommon blue obsidian, treated material, or non-geological glass/slag; the image alone cannot distinguish these confidently.
Uses & applications
Used for ornamental objects, lapidary work, beads, carvings, and historically razor-sharp tools and projectile points. Valuable examples are transparent, vividly colored, patterned, or snowflake-bearing.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks a crystal lattice. Fresh fractures can be sharper than surgical steel.
Field identification & locations
Check for uniformly conchoidal fracture, glassy luster, and absence of bubbles; abundant round bubbles or flow texture may suggest slag or manufactured glass. Common sources include Mexico, the western United States, Armenia, Iceland, and Italy.
