Tumbling Small Obsidian

I was one of the winners in the box of rocks give away memorializing Jean (see link below).   Have been busy but finally getting to this material.   Thank you again to the anonymous contributor of the boxes.   Included in the box was about 5 pounds of very small obsidian (averaging somewhere between 1/4 and 1/2 inch size).   There were mostly broken pieces (not rounded) so I filled a 3 pound Lortone tumbler, added 3 tablesoons of 80 grit, and tumbled for a week.   I took them out this morning and there wasn't much wear on them plus I think I had a lot of grit that wasn't worn much (it could have come from a couple other barrels but I haven't ever had grit that wasn't completly gone after a week).   If I recall, I had a little less water than I might normally put in.   I didn't have any gas develop to the point where I could see the barrel buldging.  

So are there suggestions on how to tumble something like this?   More water, less water?  More grit, less grit?   Run longer than a week?    I haven't done any obsidian before other than the few pieces I find here in Missouri which everyone on the forum seems to think is slag.     Any help will be appreciated. 

Thanks

Chris 

forum.rocktumblinghobby.com/thread/104702/rockpickerforever-memorial-guessing-game

PS.  Also included in the box was some tumbling sodalite.   It must be older high quality stuff.  I looked at it this morning after a week in 80 grit and it looks like it is going to be amazing.   Will post pics when I get it done.