Obsidian - Chihuahua, Mexico

A clean, uniformly black obsidian specimen from Chihuahua, Mexico. Obsidian forms when silica-rich (typically rhyolitic) lava is extruded or chilled so rapidly, often at a lava flow margin, dome edge, or where lava meets air or water, that ions have no time to organize into a crystal lattice before the melt locks solid. The result is a true volcanic glass: amorphous at the atomic level, with no internal crystal structure at all, which places it outside the usual mineral classification (minerals require a definite crystalline arrangement). Chemically it's essentially the glassy equivalent of granite or rhyolite, just quenched too fast to crystallize.

The defining physical trait is its conchoidal fracture: obsidian breaks in smooth, curved shell-like surfaces radiating from the point of impact, the same fracture behaviour seen in other glasses and in fine-grained cryptocrystalline materials like chert and flint. This is a solid teaching piece for illustrating amorphous vs. crystalline solids, rapid-cooling igneous textures, and fracture mechanics side by side with true crystalline igneous rock, a natural comparison piece if you're building out a systematic rock/mineral reference set or classroom kit.

That same conchoidal fracture behaviour is exactly what makes obsidian a longstanding favorite for lapidary work and flintknapping, it takes an extremely sharp edge when struck correctly (obsidian blades can exceed the edge sharpness of surgical steel) and cabs/polishes to a glossy black finish. If that's your intended use, this piece will work fine for it, but it's being offered here primarily as a geological reference/display specimen rather than pre-selected knapping material.

*Please note: Specimens may have sharp edges due to the nature of the material and should be handled carefully to avoid any injury*

Specimen Details

Approx. specimen weight (g): 982 grams

Approx. specimen size (mm): 140mm x 105mm x 55mm