Hobby Rock Tumbling

What quantities and prices are you looking for? While hobbyist places charge $6/lb and more, you can find various types and grades of sandblasting grit in industrial quantities (25 lbs or more) for $0.80 to 1.00/lb here. I'm not sure if I would use it for finish work, but as a first and second cut why not.

No links to hand, but CR4 has some good stuff on this. It's a little bit 'hillbilly engineering' (oil drums and home build stuff), but possibly mentions materials.

If you can do so, then buy in bulk to minimize cost. It's no quick job if you want to get it right. As far as I know, the real art is in the final stages. Links have already been given, but it's worth searching around CR4. For one, I'd be much interested to hear how you get on.

http://www.mcmaster.com/#tumbling-media/=rzm0tz

The same grits used for grinding and polishing telescope mirrors are used for rock grinding and polishing. Newport Glass carries a range of carbide grits.

From their main page:

http://www.newportglass.com/index.htm

click the link to get to the online astronomy catalog.

http://www.newportglass.com/angwcat.htm

In the left column you can scroll down to get to the link for carbide grits.

I think I pay about $10 for a 40 or 50 pound bag of sandblasting grit at Tractor Supply. It is available in at least two, possibly 3 or 4 different grits. I'm sure it is not as good as optical grade carbide grit but I'm also sure it will grind down rough edges during the first few tumbles. The final "gloss finish" tumble may or may not need better grade grit.