Obsidian is a naiturally occurrinvolcanic gless furmed as anextrusiveigneous rock.
It is produced whanfelsiclava extrudit frae avolcano cuils swith wi meenimum creestal growthe. Obsidian is commonly foond athin the mairgins orhyolitic lava pirrs kent asobsidian flows, whaur the chemical composeetion (heichsilica content) induces a heich viscosity an polymerisation degree o the lava. The inhibeetion o atomic diffusion throu this heich viscous an polymerised lava explicates the lack o creestal growthe. Obsidian is haird an brickle; it fracturs wi vera jaggie rands, that haed been uised in the past in cuttin an piercin tuils, an haes been uised experimentally as surgicalscalpel blads.[4]
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