Volocano Island -missing one obsidian

[number1mimi]

I am back doing some clean up on some islands, I found I had found all but one of the obsidian stones, or what every they are, I have been looking for this one off and on for three days... :confused: any ideas???

[Cyberomega]

You might have built a building on top of one.

[number1mimi]

I found it under a tower...