AO is about as good as it gets for Mohs 7 rock tumbler. for softer obsidian for instance I believe a softer abrasive would speed things up.
A question you could pose for tumbling - Mohs 9 abrasive for Mohs 7 rock. Mohs 7 abrasive for Mohs 5 rock. For finishing(not coarse grind)
The guys run 50% aluminum oxide ceramic media with obsidian. I believe it is the Mohs 9 media that is smoothing the aluminum oxide and NOT the obsidian. And it takes a long time.
I believe Mohs 3-4-5 rock would be a fast and easy run if you had softer abrasives so the soft rock can round off(smooth the abrasive).
I believe Mohs 9 AO is a terrible match for finishing softer rocks. Tooooooo haaaard
I believe soft rocks would be a fast and easy finish tumble with softer finish abrasives.
Because tumbling depends on the rocks to 'smooth' or break down abrasive.
do you think calcite is going to break down 1000 grit diamond ? No no no no.
do you think calcite is going to break down 1000 grit alum ox ? No no no no
do you think agate is going to break down 500 grit alum ox ? darn right it will, especially with the higher dynamic forces(or higher rate of forces) in a vibe.
I have thought about attacking the 'tumbling soft rock problem'. Need some softer abrasives - no idea where to start.
The overseas guys tumble soft stuff to a wet finish regularly. if they can, we should be able.
BECAUSE, the coarse grind would take a week instead of 2 months with soft rock. GREAT !
Now we need a soft finishing abrasive.
If we could tumble so many fine soft rocks it would revolutionize tumbling and get rid of the long coarse grind step because soft rocks grind super fast with SiC 30-46-60-80 -- great.