Not meaning to sound pedantic, but Obsidian is NOT crystallized lave, on the contrary. It is lave that cooled so quickly that it did not have the time to crystallize out, which is why it is sometimes called volcanic glass.
1 environment (among others) one could think of is lava that erupts under water in the sea, where it cools very quickly. In that environment it can take a peculiar shape while cooling down, and it forms “pillow lave”: the rock then consists of rounded sections reminiscent of pillows.
Examples of lava that has had time to crystallize is granite, basalt, and many others.