I can tell you if you leave a bag of quickrete outside, it will turn into a bag-shaped rock.

Check out the Hypertufa forum. There are lots of people there making rocks.

I pour thick construction cement mix into cream puffs' containers and get square stones/tiles. Mix has to be rather thick and will take a while to set. I know this is less artsy than Hypertufa.

See Wendy2shoes postings under that forum and her posted pictues how she makes her own rocks. I'd love to try her method this summer.

Wendy2shoes...thanks for the explanation. Now it seems clearer to me what needs to be done.

I used to have an article that Martha Stewart wrote on making cement stepping stones from large plant leaves (e.g., elephant ears). Not exactly a bag of rocks, but just throwing that out there, just in case anyone is interested.

Aha, before posting this, I did a search and found an article. It's not THE article but the link second link below is a how-to and the first one is an example picture.

Sample picture: http://bit.ly/xkZ3NE

Here is a link that might be useful: Making Cement Leaves

A couple of years ago while working on our patio, we mixed up some cement to use on a new section. Somehow we miscalculated the amount that was needed and ended up with too much concrete. Since I was not sure how to dispose of a big concrete lump, I formed the stuff into small manageable rocks and laid them on top of an old tarp to dry. The rocks ended up being fairly round with flat bottoms and when they were dry it was easy to peal them off the tarp. I ended up using them as a border for the perennial garden where they look great mixed in with the other rocks.

Any pictures of those rocks? Would love to see them.

I would absolutely LOVE to make a frame to make a mosaic simular to this one! http://www.instructables.com/id/A-Backyard-Path-that-says-Were-going-Places/

Here is a link that might be useful: Beautiful walkway