This piece of obsidian is from the National geographic rock Tumbler set which we have purchased more than once. It has a flat edge indicating that has been cut from a larger block.
It's not that we don't tumble international rocks, it is more that we have so many Scottish rocks to tumble that we will never ever get the chance to polish these ones. And so we are opening them up to you. 
I do not know where this obsidian came from, I only know that it was part of the nat Geo set and therefore will have at least some ethical collection policies. 
Obsidian itself as a form of glass made when volcanic material meets other minerals, such as sand. 
In terms of crystal healing obsidian as one of my favorite materials. Neither crystal nor rock nor technically tectite, carrying an obsidian crystal with you is said to clear out those things in your life which are not for you and bring in things that are. 
It was moldavite before moldavite was moldavite...