Obsidian (/əbˈsɪdi.ən, ɒb-/ əb-SID-ee-ən ob-) is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.
For starters, the nearest land mass is Russia: The slightly larger Big Diomede Island is just over two miles away, within eyeshot of the Alaskan villagers.