lava extruded from a volcano cools rapidly with very little crystal growth. Obsidian
is mineral-like, but not a true mineral because as a glass it is not crystalline and its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid, that is an amorphous substance lacking a systemic internal arrangement of atoms. This explains the wild variations in color seen in the slices above in addition to the fact that long ago this was a flowing liquid! Do you see an owl or a gremlin?
